After its acceptance into service in 1961, the PKT (GRAU index 6P7) was used as the standard machine gun for enclosed Soviet armoured fighting vehicles. Mass production of the PKT began at the Kovrov Mechanical Plant in 1963, one year after production of the PK began, although the technical documentation for the entire PK family had been completed by 1961. The PKT weighs 10.5 kg, making it slightly heavier than a PK (9.0 kg), despite having no buttstock or pistol grip. The first and most obvious visual differences that distinguish a PKT from a PK are the absence of a buttstock, pistol grip, trigger, ammunition box bracket, bipod mount and sights. Instead, a solenoid trigger unit is riveted to the rear of the receiver, replacing the riveted buttstock and trigger group, with a large round solenoid protruding behind the receiver and a mounting hole located where the trigger group used to be, allowing the PKT to be installed on the existing two-point mounts for SGMT machine guns. In total, only 14 out of 30 units and only 96 out of 176 parts were shared with the PK, as shown in the image below. That said, this comparison is purely technical as it accounts for even small differences in details, such as the gas regulator, flash hider, absence of an ammunition box bracket, absence of Stepanov tripod mounting points, and so on. The nature of this type of comparison can be seen in how the number of units shared between a PK and a PKN are tallied, and why it only shares 27 units with the PK despite having an identical number of parts (176). Keeping in mind that the PKN structurally differs from the PK only in having additional drilled holes to rivet a dovetail mount on its receiver body, this apparently constituted enough of a change that 3 units were considered to be no longer unified.
The changes implemented to create the PKT were, overall, quite major from a structural interchangeability standpoint, as it reduced the degree of production commonality between the PKT and its parent design and made direct conversions impossible. Nevertheless, this did not affect the interchangeability of operating parts which may require replacements in the field, such as the bolt carrier assembly, barrel locking wedge, charging handle, feed mechanism, and so on.
The PKT was also designed with mounting points compatible with the SGMT, which did not differ from the SG-43. As a result, the PKT is compatible with the existing reciprocating shock absorber on tank coaxial mounts originally made for the SGMT. All in all, the changes from the PK to the PKT were generally beneficial adaptations to optimize the weapon for its role, and allowed the PKT to be used interchangeably with both the PK family and the SGMT.
When linked to an electric firing system, the machine gun can be fired either by depressing the trigger button on the gunner's control handles or by pressing the manual trigger button located on the solenoid trigger unit installed at the back the receiver of the machine gun. The latter method may be necessary if the tank loses electrical power or if some other issue makes it impossible to fire the machine gun normally. The solenoid trigger unit works simply by lowering the sear with a solenoid actuator via a linkage.
For the purposes of a tank coaxial machine gun, the design of the PKT and PKTM can be considered exemplary as it has an unusually short and compact receiver compared to its direct foreign counterparts (excluding purpose-built machine guns like the M73 and M219), although this was primarily beneficial in lightening the machine gun rather than an adaptation for enclosed spaces, and in practice, there is no significant advantage because the solenoid trigger unit adds to the length of the receiver. The forward location of the belt feed is also not conducive to fitting inside enclosed spaces, as the feedway determines how far forward the machine gun can be mounted, with the distance between the feedway and the rear end of the receiver being the critical factor for compactness in enclosed spaces. Rather than shortening the machine gun for enclosed spaces, this layout facilitated a short receiver with a convenient amount of clearance between the trigger guard and the ammunition box in the PK or PKM when used in the light machine gun role. In spite of this, the PK design still has a shorter length between the rear of its receiver and its feedway than machine guns like the FN MAG.
For the purposes of a tank coaxial machine gun, the design of the PKT and PKTM can be considered exemplary as it has an unusually short and compact receiver compared to its direct foreign counterparts (excluding purpose-built machine guns like the M73 and M219), although this was primarily beneficial in lightening the machine gun rather than an adaptation for enclosed spaces, and in practice, there is no significant advantage because the solenoid trigger unit adds to the length of the receiver. The forward location of the belt feed is also not conducive to fitting inside enclosed spaces, as the feedway determines how far forward the machine gun can be mounted, with the distance between the feedway and the rear end of the receiver being the critical factor for compactness in enclosed spaces. Rather than shortening the machine gun for enclosed spaces, this layout facilitated a short receiver with a convenient amount of clearance between the trigger guard and the ammunition box in the PK or PKM when used in the light machine gun role. In spite of this, the PK design still has a shorter length between the rear of its receiver and its feedway than machine guns like the FN MAG.
Russian firearms expert Max Popenker credits this to the two-stage feeding mechanism of the machine gun, inherited from the Maxim, where the belt is fed into the gun from above the trunnion and a fresh cartridge is pulled out of its belt link and positioned behind the chamber before it is loaded rather than a simpler single-stage feed with the cartridge being directly pushed through its link and into the chamber in a single motion when feeding.
Officially, the nominal maximum range of the PKT(M) is 4,000 meters, and its maximum sighted range is 1,300-2,000 meters on Soviet armoured fighting vehicles. The exact sighting range depends on each vehicle and is predominantly influenced by the capabilities of their sights and fire control system. When firing ball ammunition, the point-blank range for a standing man of average height (170 cm) is 700 meters. The point-blank range against a torso-sized target (height of 50 cm) is 440 meters, and the point-blank range against a running man (height of 150 cm) is 670 meters. The maximum effective range against ground targets is stated to be 1,000 meters, because this is the tracer burnout range. The range of accurate fire is 800 meters. Aimed fire on point targets out to 1,000 meters is feasible when firing the PKT with the high magnification sight of a tank. For infantry machine guns relying on iron sights, there is a possibility of the gunner mistaking tracer burnout with tracer strike on the ground, making fire correction more difficult at this range.
At some point in the 1990's, the PKTM (GRAU index 6P7M) arrived in service. Originally, the PKTM had been created on the basis of the PKM machine gun during its development and was ready for acceptance in 1969, but it was not accepted into service because the production of infantry PKM machine guns was only been planned for Kovrov and the production of the PKT had already been transferred to Zlatoust, according to Ponomarev Yuri in the article "От ПК к ПКМ", published in the 2011 No. 12 issue of the "Калашников" magazine. From external appearances, the changes include a new receiver with fewer rivets, replaced by spot welds, and a switch to the PKM top cover. The trunnion is still of the PK type. A PKTM is shown in the image below. This new top cover was slightly lighter than the slab-sided top cover of the original PK by being stamped from thinner sheet steel while having a structurally stronger shape, but for a tank machine gun, this change was only meaningful as far as production unification. The lightened trunnion of the PKM is not conducive for a mounted machine gun, as it decreases the heat tolerance in continuous fire, so it is understandable for the original PK trunnion to be retained. In all other regards, the PKTM remained essentially identical to the PKT, and they are normally considered as such in use.
One of the most important modifications of the PKT that distinguished it from the infantry versions was the new gas regulator mechanism. As in the infantry versions, the gas regulator is integral to the PKT barrel and not the gas tube. The same three-position adjustment functionality was retained, but the gas regulator of the PKT would not vent gasses outside the gas tube at all so that the accumulation of propellant gasses inside the armoured vehicle is minimized. On a PK or PKM, the gas regulator adjusts the amount of gas pressure acting upon the operating piston by changing the amount of gasses vented out of the regulator chamber depending on the selected position. Position "1" vented out gasses through two holes, position "2" restricted one of the two vent holes so that less gas was vented, and position "3" shut both vents so that no gasses were vented at all. On a PKT, the barrel has a narrower gas port to permit a reduced flow of gasses and the gas regulator further restricts the size of the passage into the gas tube, depending on the gas setting. The design of the gas regulator valve itself is basically the same as the SG-43 gas regulator.
Position "1" is the default setting for a clean and lubricated weapon, and the next two settings are intended for situations where the fire rate of the machine gun begins to slow down for whatever reason, typically from an increase in friction from a buildup of propellant residue in the gas system and the receiver. The higher settings progressively increase the amount of gasses that can flow into the gas tube to act upon the gas piston. Position "2" should be used after 3,000 rounds have been fired from the machine gun without cleaning, and position "3" should be used after another 3,000 rounds have been fired.
The gas regulator valve is adjusted between the three possible positions by turning the valve knob on the left side to loosen the valve, pushing it to the right to clear the alignment pin of the current setting, turning it to the desired setting, and then tightening the valve knob to clamp down the valve. To facilitate this, the end of the valve knob has a cut for a screwdriver or wrench, and the knob itself is knurled. Adjustment of the gas regulator cannot be done on the fly, like on the infantry PK or PKM, and it does not permit adjustment with the rim of a 7.62x54R cartridge like the infantry guns. The gas regulator normally does not require adjustments during combat, but if absolutely necessary, the machine gun has to be dismounted first, as the gas regulator is otherwise inaccessible.
It was not possible to completely prevent all fumes from seeping out of the machine gun through various ports and openings simply because its open-bolt operating system leaves the mouth of the empty chamber open, but the PKT has an advantage over many other GPMGs because the ejection port is sealed by a spring-loaded flap until the moment of ejection. This can reduce the amount of fumes that exit the weapon by some amount. It is worth noting that the MAG 60-40, the tank coaxial variant of the MAG 58 infantry machine gun, does not have a closed gas regulator, so tank coaxial mounts for the MAG 60-40 need to be designed with widened barrel port and a seal so that gasses are not vented into the crew compartment.
The cyclic rate of fire of the PKT and PKTM is 700 to 800 RPM. The firing rate was increased from the 650 RPM rate of the PK and PKM primarily because it was determined to be optimal for a mounted machine gun, where recoil control is a non-issue. For such a weapon, the deciding factor was that a large supply of ammunition could be carried aboard the armoured vehicle so a higher rate of fire provided a more rational compromise between a variety of requirements including ammunition conservation, hit probability on infantry targets, fire correction, barrel heating rate, and so on. Additionally, a rate of fire of around 700 RPM matches the rate of fire of the SGMT machine gun, and as such, allows the PKT to be fitted onto shock absorbing mounts intended for the SGMT without unintended destabilization, as shock absorbers have to be tuned to the rate of fire and recoiling characteristics, since the recoil pulses are periodic in nature. With all other operating parts being interchangeable with the infantry PK and PKM, the higher rate of fire of the PKT was provided by the unvented gas regulator and the longer dwell time from the lenghtened barrel. The bolt carrier is driven to a higher velocity by the gas impulse, and thus, reciprocates more quickly.
In practice, the PKT(M) was specified to have an average fire rate of 250 rounds per minute. The bullets fall to a transonic speed at a range of around 700 meters and fully transition to subsonic flight at a range of around 850-860 meters. With the shift from supersonic flight to subsonic flight, the dispersion characteristics can suffer due to the shift in the center of pressure due to the change in the airflow characteristics. This is a characteristic of virtually all bullets designed for supersonic flight, and is a consequence of the aerodynamic design of such bullets being optimized for a supersonic flight regime. It is likely that since consistent dispersion performance is only guaranteed up to a nominal distance of around 860 meters, 800 meters is considered the effective range of the PKT(M) against point targets, taking into account the greater air density in very cold conditions. The maximum effective range against ground targets is considered to be 1,000 meters. Firing at ground targets from longer ranges is possible, albeit with reduced accuracy, so in general, only area targets should be engaged. Based on these metrics, the PKT has a slightly longer reach than its equivalents chambered in 7.62x51mm, to the order of 50-100 meters. The margin of this advantage is small enough that in practice, there is essentially no real difference.
As a reference, it is worth noting the different design approaches of the historical counterparts to the PKT(M) used by the hypothetical adversaries to the Soviet Army. In the Bundeswehr, the MG3 was used in a variety of roles, including as a tank coaxial machine gun. In a mounted configuration, the machine gun is normally set to its highest fire rate of 1,200 RPM, but despite the high cyclic fire rate of the MG3 compared to all other machine guns of its class, its practical fire rate was only 150 RPM due to the low heat limit of its rather light barrel. Moreover, due to the constraints of the mounting system in tanks and other armoured fighting vehicles, it was not possible to overcome this shortcoming by periodically swapping out barrels as with infantry guns, and the MG3 was not equipped with a heavy barrel. So despite its high cyclic rate of fire, the MG3 did not actually have a relevant fire rate advantage, and moreover, may have had to run at its heat limit more often when used in armoured vehicles than when it was used in infantry roles due to the inability to swap barrels.
As another point of comparison, the MG34, used in the Wehrmacht during the war as a tank coaxial and bow machine gun, had a rate of fire of 800-900 rounds per minute. Contrary to the popular opinion that the MG34 was retained for coaxial and bow machine guns for German tanks like the Tiger II and Panther despite the appearance of the MG42 due to its unique quick-change barrel mechanism being more suitable for the confined space of an enclosed vehicle, the fact is that the MG34 mount on such vehicles made it impossible to carry out a barrel swap. While barrel swaps were possible in a Pz.III due to the machine gun being mounted by the shroud rather than the receiver, this capability was deleted from later vehicles. In both a rail mount for coaxial machine guns and a ball mount for bow machine guns, the MG34 (with a Panzerlauf) was not only rigidly attached to the mounting frame at the trunnion but also at the rear of the receiver underneath the trigger assembly, making it impossible to rotate the receiver around its hinge to access the barrel without dismounting the machine gun entirely. A heavy barrel was not installed in these MG34s because the machine gun operated on the short recoil principle, and a heavier barrel would have affected the dynamics of the operating mechanism and its rate of fire. As such, these machine guns retained the standard 2 kg barrel, which had a heat limit of 250 shots fired continuously in bursts.
In the U.S Army, machine guns with a low cyclic rate were historically preferred as a technical measure to prevent excessive ammunition expenditure, and in fact, in 1973-1974 when the U.S Army initiated plans to replace the M219, a limit of 400-625 RPM was set as the by the so-called Required Operational Capability and a lower fire rate within the specified range was preferred. The historical preference for a low firing rate can be seen in the M1919 or M37 machine guns which were built with a cyclic rate of fire of 400-500 RPM. The later M73 and M219 machine guns had a marginally higher rate of fire of 500-625 RPM, which was a much more reasonable range. The barrel weighed 2.55 kg, which is good given that it is only 559mm long. Its average cross sectional thickness should therefore exceed that of a PK and MAG 58 by a comfortable amount and reach or even exceed that of a PKT. Moreover, the M73 and M219 were specially designed for enclosed AFVs and was not only exceptionally compact, but it also had a mounting system that permitted quick barrel swaps using a mechanism similar to the MG34, as demonstrated in a U.S Army training film. Overall, the M73 and M219 were ostensibly ideal machine guns for enclosed AFVs and appear to be the top candidates as the best in their class.
However, a major caveat to this impressive capability is that both of these machine guns were plagued by issues that may be charitably described as inconsistent reliability, which may or may not have been design faults, but were nevertheless grounds for their eventual retirement. They were replaced by the M240, a licence-produced version of the FN MAG 60-40 machine gun under a different name.
Outside of the USSR, the MAG was the most successful counterpart to the PKT, and it is perhaps not a coincidence that it shared the closest resemblance in technical characteristics, including rate of fire. The MAG 60-40 had a rate of fire of 650-950 RPM. Under normal operating conditions, the fire rate is practically the same as the PKT.
The rifling of the PKT(M) barrel has 4 rectangular lands and grooves with one right-hand twist in 240mm. The barrel weighs 3.23 kg which is 0.61 kg heavier than the barrel of a standard PK (2.62 kg) and 0.83 kg heavier than that of a PKM (2.4 kg). The barrel length of the PKT is 722mm, of which 665-666mm is rifled. The standard PK barrel weighs 2.6 kg and has a length of 603mm, of which 550mm is rifled. The PKM barrel (2.4 kg) was noticeably lighter than the PK barrel due to the removal of the fluting and a slight reduction in thickness. These weight figures refer to the barrel alone, not including muzzle attachments, the front sight post, the gas regulator, or the carrying handle. It may not be comparable to the barrel weight figures stated for other machine guns, as they often refer to the barrel assembly rather than the barrel alone. For example, the MAG 58 has a barrel assembly weight of 3.05 kg, but on the M240, which has an identical barrel, the barrel alone is 2.49 kg (5.5 lbs).
Proportionately, the specific weight of a PKT barrel is slightly heavier than a PK barrel, weighing 44.7 grams per centimeter of length while a PK barrel weighs 43.3 grams per centimeter, and it is slightly lighter than a MAG barrel, which weighs 45.1 grams per centimeter. Due to the longer barrel, the PKT fires at a slightly higher muzzle velocity than the PK, which had a marginal effect on its effective range. However, this was not the reason why the the barrel length was increased. The primary reason was to match the barrel length of the SGMT medium machine gun which was 720mm in length. The SGMT machine gun shared the same barrel length of the SGM it was derived from, and both had very heavy barrels (4.1 kg) as they were medium machine guns whereas the PK was a general-purpose machine gun with a shorter and lighter barrel to optimize it for infantry use. The increased barrel length of the PKT enabled it to achieve the same muzzle velocities as the SGMT when firing the same ammunition, thus ensuring the possibility of replacing the SGMT in older AFVs with the new PKT without any modifications to the gunner's sights. The positive effect on the effective range of the machine gun was merely a bonus. Compared to the SGMT, with a specific barrel weight of 56.9 grams per centimeter, the lightened barrel of the PKT can be expected to have had a negative effect on heat endurance.
Because tank gunners do not face problems with dust obscuration and recoil control when using the coaxial machine gun, the combat rate of fire tends to be higher than the rate expected from an infantry machine gunner, but just like their infantry counterparts, tank gunners are still trained to be cognizant of the heat limits of the machine gun. Having a machine gun with a greater heat tolerance permits the delivery of sustained fire for longer periods, and this is highly desirable because the primary purpose of machine guns is the suppression of enemy forces with accurate sustained fire in support of friendly forces. In the assault, this is done to allow the maneuver of friendly forces against the objective, and in the defence, this is done to prevent the maneuver of enemy forces to facilitate their destruction. For tanks, the machine gun fulfills the same role and also serves as a close range alternative to HE-Frag shells with low collateral damage to eliminate soft targets in the open.
Assuming a robust construction, the heat tolerance of a machine gun is usually dependent on the barrel alone. Barrel overheating is a particularly pernicious issue for enclosed AFVs because of the enclosed nature of vehicle and the weak airflow inside them. Moreover, in tank turrets with thick armour, most of the barrel may be enshrouded by the gun mask or the walls of the machine gun port cutout in the turret, exemplified by the T-72A turret shown in the drawing below. The lack of fluting on the PKT barrel like on a PK barrel was most likely influenced by the realization that the lack of airflow inside a tank turret rendered such a feature almost entirely useless.
One negative design trait of the PK family in terms of heat endurance is the use of a rotating bolt locking mechanism, owing to the fact that the locking lugs of the bolt engage into recesses on the trunnion directly behind the barrel. During intensive fire, carbon deposits build up much more rapidly on these locking recesses compared to the locking surfaces of other types of locking mechanisms, such as shoulders built into the receiver wall like in the SG-43 or in Degtyarev flapper-locked guns, and the receiver floor plate or crossbar in tilting lever guns (BAR, FN MAG, FN FAL) and in tilting bolt guns (LK vz. 26). Although the bolt face itself is not intensely polluted, the carbon build-up may cause bolt jamming issues, requiring either an adjustment of the gas regulator or emergency cleaning of the locking recesses.
The barrel of the PK is rated for 500 shots fired continuously in bursts at the practical rate of fire of 250 rounds per minute before a barrel change is mandatory. After 1,000 rounds of continuous fire in this fashion, the entire machine gun must be left to cool. A manual on the operation of the PK family of machine guns defines a short burst as lasting for 10 rounds and a long burst as lasting for 30 rounds. This is practically the same as the 20 or 30-shot burst lengths specified for other machine guns in foreign armies.
The thicker and longer barrel of the PKT retained the same heat limit of 500 shots fired continuously in bursts. Because the PKT is fed with 250-round boxes, this is equivalent to a continuous burst fire limit of two ammunition boxes before firing must halt in order to avoid premature wear of the barrel and prevent a drop in accuracy from overheating. This is good performance for a coaxial machine gun and it is particularly good when compared to weapons like the MG3, but it is principally the same as heavier machine guns like the FN MAG. The MAG 60-40 and M240 have a 2.49 kg barrel, unified with the MAG 58 infantry variant except in the lack of a front sight, and for these guns, a barrel change is required after 10 minutes of fire at the nominal sustained rate (100 RPM) or after 2 minutes of fire at the nominal rapid rate (200 RPM), equivalent to 400 shots fired continuously in bursts. The M60 machine gun also had a heat limit of 400 shots fired continuously in bursts at the same nominal rapid fire rate of 200 RPM. Such a direct comparison may not be completely valid due to possible differences in the criteria for the heat limit, but broadly speaking, this serves as a reasonable indicator of the heat limits of these machine guns.
On all Soviet tanks from the T-55A to the T-80U and in modern Russian tanks like the T-90A, the PKT or PKTM would be fed with 250-round boxes of belted ammunition linked in 50-round segments. Each 250-round box weighs 9.4 kg fully loaded.
The LPS bullet is a light ball bullet with a mild steel core. The bullet has a weight of 9.6 g and has a muzzle velocity of 855 m/s when fired from the PKT. Between the steel core and the jacket is a lead filler. Its purpose is to help seat the core, but it also functions as additional mass at the circumference of the bullet which increases the rotational inertia of the bullet. This allows the bullet to remain spinning at a sufficient rate to remain stable at longer distances than would be otherwise possible without the lead filler.
The LPS entered service in the Soviet Army in 1953 as a universal ball bullet for rifles and machine guns. At the same time, the production of ammunition with L bullets (light ball with lead core) and D bullets (heavy ball with lead core) was discontinued. The standardization of bullets had a significant economic effect as it allowed Soviet ammunition production facilities to be optimized for a single product, and the shift to a new ball bullet with a steel core also brought long-term cost savings by conserving lead.
Moreover, the LPS bullet had superb ballistic properties that allowed it fulfill the function of heavy ball bullets while having a bullet of the same weight as light ball bullets. The weight of the LPS bullet, 9.6 grams, was identical to the L obr. 1908/30 light ball bullet with a lead core which had a muzzle velocity of 855 m/s when fired from an SG-43 or SGM medium machine gun. The D obr. 1930 heavy ball bullet weighed 11.8 grams and had a muzzle velocity of 800 m/s when fired from an SG-43 or SGM. The maximum range of the L bullet was 3,800 meters whereas the D bullet achieved a maximum range of 5,000 meters, matching the .30 cal M1 ball round, which weighed 11.3 grams and had a muzzle velocity of 807 m/s when fired from a 24" barrel. The maximum range of the LPS bullet when fired from an SG-43, SGM, or PKT at a nominal muzzle velocity of 855 m/s is 4,600 meters.
The L bullet produced less recoil, and was best suited for short to medium range direct fire from light machine guns and infantry rifles. The D bullet was optimized for long range fire from medium or heavy machine guns against area targets using indirect fire techniques. It also provided better long range direct fire performance in terms of dispersion and lethality. However, the role of heavy bullets was deemed obsolete when actual combat experience during the early stages of the so-called Great Patriotic war showed that long range fire from machine guns was a waste of ammunition which was only exacerbated if indirect fire was used.
However, there is no apparent connection between receiver length and the number of stages in the feeding mechanism, as both pull-out and push-through mechanisms ultimately involve the same pushing motion to feed a cartridge into the chamber. Instead, the primary features responsible for the short length of the PK receiver are the short length of the bolt and bolt carrier behind the breech face of the barrel, and the use of the sides of the bolt carrier as the camming surfaces for the feed pawl rocker arm. Unlike the conventional type of feed mechanism found on many machine guns, where there is a long cam track interfacing with a roller along the top cover to articulate the rocking feed pawl, the PK has a simpler and much more compact form of the same basic mechanism, driven in reverse; the cams are on the rocking arm of the feed pawl, and the camming surfaces are cut into the sides of the bolt carrier. In this way, the cams for the feed pawl do not compete for space on the top of the receiver. During the recoil stroke, the left side of the bolt carrier pushes on the roller, driving the rocker arm and the feed pawl to the left. During the return stroke, the rocker arm and the feed pawl are driven to the right by the right side of the bolt carrier, which has the same cut as the left side, only reversed.
The small and short bolt, inherited from the AK, is rather light, which in turn enabled a lighter bolt carrier to be implemented in the design while maintaining a sufficiently high inertial mass ratio between the carrier and the bolt, and the necessary mass in the bolt carrier was achieved by distributing a greater mass of metal thickness at the base of the carrier and at the hinge of the gas piston, in addition to the solid gas piston itself. The length of the bolt carrier - aside from the gas piston) is also very short, being long enough only to guide the stem of the bolt. The short length of the bolt and bolt carrier meant that there was minimal length extraneous to the recoiling distance. This significantly shortened the total length of the receiver compared to machine guns like the FN MAG and M60, which have a very long bolt in addition to a long bolt carrier body behind the bolt, resulting in long receivers without a correspondingly longer recoiling distance.
In turn, the belt feed mechanism of the PK was the main reason why the short bolt carrier could be made so short. The rocker arm of the feed pawl, designed to tilt leftward to pull the belt in and tilt rightward to reset, has a simple skid for the camming surface on the right side of the bolt carrier and a roller for the camming surface on the left side of the bolt carrier. A critical feature of this layout is that the rocker arm is at the same longitudinal position on the receiver as the belt, whereas conventional feed systems require the cam track to be behind the feed tray. This feed mechanism is conceptually and mechanically similar to that of the Holek feed mechanism used in the Czechoslovakian TK vz. 37 and UK vz. 59 machine guns. It primarily differs in that the rocker arm engages different sides of the bolt carrier depending on whether it is recoiling rearward or returning forward, and that a roller is present on the rocker arm for the recoiling stroke. These features provide a rational distribution of pulling effort and mechanical stress, and greatly reduce surface wear.
By engaging the left side of the bolt carrier when pulling the belt, a longer lever for the feed pawl is obtained from the rocker arm, so the torque available from the momentum of the recoiling bolt carrier is enough to reliably feed a belt through the gun even if there is unusually high resistance. In fact, as the drawing above shows, the lever arm for the roller is more than twice as long as the lever arm for the skid. Conversely, in the UK vz. 59, the rocker arm is shorter than even the lever arm for the skid in a PK, so a heavy and fast-moving bolt carrier assembly is needed to supply the torque needed to reliably pull a belt. Additionally, the use of a roller instead of a skid changes the interaction from sliding friction to rolling friction, which significantly reduces friction. This addresses the issue of the high reaction forces encountered when pulling a belt under high resistance. The lack of a roller on the rocker arm for the return stroke can be explained by the fact that the belt does not move as the pawl moves rightward to reset, so the reaction force on the sliding surface - and thus the sliding friction force - comes purely from overcoming the inertia of the rocker arm and depressing the spring in the feed pawl as it slides below the next cartridge in the queue. Since the rocker arm is very light and the feed pawl spring is soft, this reaction force is tiny, and so the wear on the camming surfaces is almost negligible. The rocker arm itself is not spring loaded; its motion is entirely controlled by its points of contact with the camming surfaces.
Additionally, it is worth noting that in the PK feed mechanism, the impulse on the feed pawl (and the belt being pulled along by it) is managed by the long, gently curved cam surface on the bolt carrier acting over the entire recoil stroke, with the pawl advancing the belt in parallel with the de-linking of a cartridge. For machine guns with a high rate of fire, the angle of the cam track should be as small as feasible to offset the high bolt carrier reciprocating velocity, because the belt should be advanced with a low impulse; with a large force to overcome the weight of a hanging belt and various resistances, but delivered over a longer time so as to reduce the stress on the feed mechanism, particularly parts that experience sliding friction such as the cam track and the feed pawl. This is not necessarily a major issue for feed reliability in general, but it is desirable for machine guns with a high rate of fire. For instance, the MG42 feed mechanism, which had to cope with a cyclic rate of up to 1,500 RPM, was designed to advance the belt in two motions; once when the bolt recoils, and once when it returns into battery.
In the PK action, the loaded segment of the belt (right side) is advanced from the moment the bolt carrier begins moving, but the empty segment of the belt (left side) is only pushed out once the next cartridge in the queue is completely de-linked. This means that during the extraction period, the second cartridge in the queue bunches up against the belt link of the first cartridge in the queue, which is permissible due to the long pitch and hinged design of the non-disintegrating Maxim style belt, permitting rotation of a pair of links around their cartridges and around their hinge joint.
With most other feed mechanisms, the belt cannot be advanced while feeding so as not to interfere with the de-linking of the cartridge, since the downward orientation and free expansion of the open side of the link are critical factors for reliable cartridge de-linking. Because of this, the bolt carrier can only begin camming the feed pawl into motion after it has already traveled far enough while stripping the cartridge for it to clear the belt link. Because the cam is on the top surface of the bolt carrier, the space needed for this free motion can only be provided by lengthening the receiver. This can be seen in the feed mechanism cams of the MG42, Browning M1919, RPD, and even indirectly in the RP-46. The sacrifices in receiver length (and by extension, mass) are practically unavoidable, as shown by the UKM-2000, a Polish redesign of the PKM to use a push-through feed with an MG42 feed mechanism. The receiver height remained unchanged, while the receiver was greatly lengthened and the bolt carrier also became much longer due to the need for a roller behind the feed tray to run in the cam track. The result was a machine gun that weighed almost a kilogram more than the PKM and was longer by 43mm (1,203mm vs 1,160mm), despite the barrel being shortened by 105mm.
Officially, the nominal maximum range of the PKT(M) is 4,000 meters, and its maximum sighted range is 1,300-2,000 meters on Soviet armoured fighting vehicles. The exact sighting range depends on each vehicle and is predominantly influenced by the capabilities of their sights and fire control system. When firing ball ammunition, the point-blank range for a standing man of average height (170 cm) is 700 meters. The point-blank range against a torso-sized target (height of 50 cm) is 440 meters, and the point-blank range against a running man (height of 150 cm) is 670 meters. The maximum effective range against ground targets is stated to be 1,000 meters, because this is the tracer burnout range. The range of accurate fire is 800 meters. Aimed fire on point targets out to 1,000 meters is feasible when firing the PKT with the high magnification sight of a tank. For infantry machine guns relying on iron sights, there is a possibility of the gunner mistaking tracer burnout with tracer strike on the ground, making fire correction more difficult at this range.
In terms of firing precision, the performance of the machine gun may vary depending on the mount upon which it is fitted. When installed on the various fixed mounts used in Soviet armoured vehicles, mainly coaxial mounts, the dispersion of the PKT(M) is considered normal if 8 rounds from a 10-round burst (80%) fit within a 14 x 16 cm rectangle at 100 meters. Machine guns that do not meet this standard are subject to an armoury-level teardown for corrective action, or replacement.
At some point in the 1990's, the PKTM (GRAU index 6P7M) arrived in service. Originally, the PKTM had been created on the basis of the PKM machine gun during its development and was ready for acceptance in 1969, but it was not accepted into service because the production of infantry PKM machine guns was only been planned for Kovrov and the production of the PKT had already been transferred to Zlatoust, according to Ponomarev Yuri in the article "От ПК к ПКМ", published in the 2011 No. 12 issue of the "Калашников" magazine. From external appearances, the changes include a new receiver with fewer rivets, replaced by spot welds, and a switch to the PKM top cover. The trunnion is still of the PK type. A PKTM is shown in the image below. This new top cover was slightly lighter than the slab-sided top cover of the original PK by being stamped from thinner sheet steel while having a structurally stronger shape, but for a tank machine gun, this change was only meaningful as far as production unification. The lightened trunnion of the PKM is not conducive for a mounted machine gun, as it decreases the heat tolerance in continuous fire, so it is understandable for the original PK trunnion to be retained. In all other regards, the PKTM remained essentially identical to the PKT, and they are normally considered as such in use.
One of the most important modifications of the PKT that distinguished it from the infantry versions was the new gas regulator mechanism. As in the infantry versions, the gas regulator is integral to the PKT barrel and not the gas tube. The same three-position adjustment functionality was retained, but the gas regulator of the PKT would not vent gasses outside the gas tube at all so that the accumulation of propellant gasses inside the armoured vehicle is minimized. On a PK or PKM, the gas regulator adjusts the amount of gas pressure acting upon the operating piston by changing the amount of gasses vented out of the regulator chamber depending on the selected position. Position "1" vented out gasses through two holes, position "2" restricted one of the two vent holes so that less gas was vented, and position "3" shut both vents so that no gasses were vented at all. On a PKT, the barrel has a narrower gas port to permit a reduced flow of gasses and the gas regulator further restricts the size of the passage into the gas tube, depending on the gas setting. The design of the gas regulator valve itself is basically the same as the SG-43 gas regulator.
Position "1" is the default setting for a clean and lubricated weapon, and the next two settings are intended for situations where the fire rate of the machine gun begins to slow down for whatever reason, typically from an increase in friction from a buildup of propellant residue in the gas system and the receiver. The higher settings progressively increase the amount of gasses that can flow into the gas tube to act upon the gas piston. Position "2" should be used after 3,000 rounds have been fired from the machine gun without cleaning, and position "3" should be used after another 3,000 rounds have been fired.
The gas regulator valve is adjusted between the three possible positions by turning the valve knob on the left side to loosen the valve, pushing it to the right to clear the alignment pin of the current setting, turning it to the desired setting, and then tightening the valve knob to clamp down the valve. To facilitate this, the end of the valve knob has a cut for a screwdriver or wrench, and the knob itself is knurled. Adjustment of the gas regulator cannot be done on the fly, like on the infantry PK or PKM, and it does not permit adjustment with the rim of a 7.62x54R cartridge like the infantry guns. The gas regulator normally does not require adjustments during combat, but if absolutely necessary, the machine gun has to be dismounted first, as the gas regulator is otherwise inaccessible.
It was not possible to completely prevent all fumes from seeping out of the machine gun through various ports and openings simply because its open-bolt operating system leaves the mouth of the empty chamber open, but the PKT has an advantage over many other GPMGs because the ejection port is sealed by a spring-loaded flap until the moment of ejection. This can reduce the amount of fumes that exit the weapon by some amount. It is worth noting that the MAG 60-40, the tank coaxial variant of the MAG 58 infantry machine gun, does not have a closed gas regulator, so tank coaxial mounts for the MAG 60-40 need to be designed with widened barrel port and a seal so that gasses are not vented into the crew compartment.
RATE OF FIRE
The cyclic rate of fire of the PKT and PKTM is 700 to 800 RPM. The firing rate was increased from the 650 RPM rate of the PK and PKM primarily because it was determined to be optimal for a mounted machine gun, where recoil control is a non-issue. For such a weapon, the deciding factor was that a large supply of ammunition could be carried aboard the armoured vehicle so a higher rate of fire provided a more rational compromise between a variety of requirements including ammunition conservation, hit probability on infantry targets, fire correction, barrel heating rate, and so on. Additionally, a rate of fire of around 700 RPM matches the rate of fire of the SGMT machine gun, and as such, allows the PKT to be fitted onto shock absorbing mounts intended for the SGMT without unintended destabilization, as shock absorbers have to be tuned to the rate of fire and recoiling characteristics, since the recoil pulses are periodic in nature. With all other operating parts being interchangeable with the infantry PK and PKM, the higher rate of fire of the PKT was provided by the unvented gas regulator and the longer dwell time from the lenghtened barrel. The bolt carrier is driven to a higher velocity by the gas impulse, and thus, reciprocates more quickly.
In practice, the PKT(M) was specified to have an average fire rate of 250 rounds per minute. The bullets fall to a transonic speed at a range of around 700 meters and fully transition to subsonic flight at a range of around 850-860 meters. With the shift from supersonic flight to subsonic flight, the dispersion characteristics can suffer due to the shift in the center of pressure due to the change in the airflow characteristics. This is a characteristic of virtually all bullets designed for supersonic flight, and is a consequence of the aerodynamic design of such bullets being optimized for a supersonic flight regime. It is likely that since consistent dispersion performance is only guaranteed up to a nominal distance of around 860 meters, 800 meters is considered the effective range of the PKT(M) against point targets, taking into account the greater air density in very cold conditions. The maximum effective range against ground targets is considered to be 1,000 meters. Firing at ground targets from longer ranges is possible, albeit with reduced accuracy, so in general, only area targets should be engaged. Based on these metrics, the PKT has a slightly longer reach than its equivalents chambered in 7.62x51mm, to the order of 50-100 meters. The margin of this advantage is small enough that in practice, there is essentially no real difference.
As a reference, it is worth noting the different design approaches of the historical counterparts to the PKT(M) used by the hypothetical adversaries to the Soviet Army. In the Bundeswehr, the MG3 was used in a variety of roles, including as a tank coaxial machine gun. In a mounted configuration, the machine gun is normally set to its highest fire rate of 1,200 RPM, but despite the high cyclic fire rate of the MG3 compared to all other machine guns of its class, its practical fire rate was only 150 RPM due to the low heat limit of its rather light barrel. Moreover, due to the constraints of the mounting system in tanks and other armoured fighting vehicles, it was not possible to overcome this shortcoming by periodically swapping out barrels as with infantry guns, and the MG3 was not equipped with a heavy barrel. So despite its high cyclic rate of fire, the MG3 did not actually have a relevant fire rate advantage, and moreover, may have had to run at its heat limit more often when used in armoured vehicles than when it was used in infantry roles due to the inability to swap barrels.
As another point of comparison, the MG34, used in the Wehrmacht during the war as a tank coaxial and bow machine gun, had a rate of fire of 800-900 rounds per minute. Contrary to the popular opinion that the MG34 was retained for coaxial and bow machine guns for German tanks like the Tiger II and Panther despite the appearance of the MG42 due to its unique quick-change barrel mechanism being more suitable for the confined space of an enclosed vehicle, the fact is that the MG34 mount on such vehicles made it impossible to carry out a barrel swap. While barrel swaps were possible in a Pz.III due to the machine gun being mounted by the shroud rather than the receiver, this capability was deleted from later vehicles. In both a rail mount for coaxial machine guns and a ball mount for bow machine guns, the MG34 (with a Panzerlauf) was not only rigidly attached to the mounting frame at the trunnion but also at the rear of the receiver underneath the trigger assembly, making it impossible to rotate the receiver around its hinge to access the barrel without dismounting the machine gun entirely. A heavy barrel was not installed in these MG34s because the machine gun operated on the short recoil principle, and a heavier barrel would have affected the dynamics of the operating mechanism and its rate of fire. As such, these machine guns retained the standard 2 kg barrel, which had a heat limit of 250 shots fired continuously in bursts.
In the U.S Army, machine guns with a low cyclic rate were historically preferred as a technical measure to prevent excessive ammunition expenditure, and in fact, in 1973-1974 when the U.S Army initiated plans to replace the M219, a limit of 400-625 RPM was set as the by the so-called Required Operational Capability and a lower fire rate within the specified range was preferred. The historical preference for a low firing rate can be seen in the M1919 or M37 machine guns which were built with a cyclic rate of fire of 400-500 RPM. The later M73 and M219 machine guns had a marginally higher rate of fire of 500-625 RPM, which was a much more reasonable range. The barrel weighed 2.55 kg, which is good given that it is only 559mm long. Its average cross sectional thickness should therefore exceed that of a PK and MAG 58 by a comfortable amount and reach or even exceed that of a PKT. Moreover, the M73 and M219 were specially designed for enclosed AFVs and was not only exceptionally compact, but it also had a mounting system that permitted quick barrel swaps using a mechanism similar to the MG34, as demonstrated in a U.S Army training film. Overall, the M73 and M219 were ostensibly ideal machine guns for enclosed AFVs and appear to be the top candidates as the best in their class.
However, a major caveat to this impressive capability is that both of these machine guns were plagued by issues that may be charitably described as inconsistent reliability, which may or may not have been design faults, but were nevertheless grounds for their eventual retirement. They were replaced by the M240, a licence-produced version of the FN MAG 60-40 machine gun under a different name.
Outside of the USSR, the MAG was the most successful counterpart to the PKT, and it is perhaps not a coincidence that it shared the closest resemblance in technical characteristics, including rate of fire. The MAG 60-40 had a rate of fire of 650-950 RPM. Under normal operating conditions, the fire rate is practically the same as the PKT.
BARREL, HEAT ENDURANCE
The rifling of the PKT(M) barrel has 4 rectangular lands and grooves with one right-hand twist in 240mm. The barrel weighs 3.23 kg which is 0.61 kg heavier than the barrel of a standard PK (2.62 kg) and 0.83 kg heavier than that of a PKM (2.4 kg). The barrel length of the PKT is 722mm, of which 665-666mm is rifled. The standard PK barrel weighs 2.6 kg and has a length of 603mm, of which 550mm is rifled. The PKM barrel (2.4 kg) was noticeably lighter than the PK barrel due to the removal of the fluting and a slight reduction in thickness. These weight figures refer to the barrel alone, not including muzzle attachments, the front sight post, the gas regulator, or the carrying handle. It may not be comparable to the barrel weight figures stated for other machine guns, as they often refer to the barrel assembly rather than the barrel alone. For example, the MAG 58 has a barrel assembly weight of 3.05 kg, but on the M240, which has an identical barrel, the barrel alone is 2.49 kg (5.5 lbs).
Proportionately, the specific weight of a PKT barrel is slightly heavier than a PK barrel, weighing 44.7 grams per centimeter of length while a PK barrel weighs 43.3 grams per centimeter, and it is slightly lighter than a MAG barrel, which weighs 45.1 grams per centimeter. Due to the longer barrel, the PKT fires at a slightly higher muzzle velocity than the PK, which had a marginal effect on its effective range. However, this was not the reason why the the barrel length was increased. The primary reason was to match the barrel length of the SGMT medium machine gun which was 720mm in length. The SGMT machine gun shared the same barrel length of the SGM it was derived from, and both had very heavy barrels (4.1 kg) as they were medium machine guns whereas the PK was a general-purpose machine gun with a shorter and lighter barrel to optimize it for infantry use. The increased barrel length of the PKT enabled it to achieve the same muzzle velocities as the SGMT when firing the same ammunition, thus ensuring the possibility of replacing the SGMT in older AFVs with the new PKT without any modifications to the gunner's sights. The positive effect on the effective range of the machine gun was merely a bonus. Compared to the SGMT, with a specific barrel weight of 56.9 grams per centimeter, the lightened barrel of the PKT can be expected to have had a negative effect on heat endurance.
Because tank gunners do not face problems with dust obscuration and recoil control when using the coaxial machine gun, the combat rate of fire tends to be higher than the rate expected from an infantry machine gunner, but just like their infantry counterparts, tank gunners are still trained to be cognizant of the heat limits of the machine gun. Having a machine gun with a greater heat tolerance permits the delivery of sustained fire for longer periods, and this is highly desirable because the primary purpose of machine guns is the suppression of enemy forces with accurate sustained fire in support of friendly forces. In the assault, this is done to allow the maneuver of friendly forces against the objective, and in the defence, this is done to prevent the maneuver of enemy forces to facilitate their destruction. For tanks, the machine gun fulfills the same role and also serves as a close range alternative to HE-Frag shells with low collateral damage to eliminate soft targets in the open.
Assuming a robust construction, the heat tolerance of a machine gun is usually dependent on the barrel alone. Barrel overheating is a particularly pernicious issue for enclosed AFVs because of the enclosed nature of vehicle and the weak airflow inside them. Moreover, in tank turrets with thick armour, most of the barrel may be enshrouded by the gun mask or the walls of the machine gun port cutout in the turret, exemplified by the T-72A turret shown in the drawing below. The lack of fluting on the PKT barrel like on a PK barrel was most likely influenced by the realization that the lack of airflow inside a tank turret rendered such a feature almost entirely useless.
This problem is intrinsically linked to the enclosed nature of gun mounts in enclosed turrets, and cannot be solved without an unconventional approach to the mount design, such as using the mount as a heat sink, compromising the armour by cutting a larger opening for a cooling shroud, or implementing dedicated forced air cooling. However, in many Soviet AFVs, one interesting feature in this regard is the use of the overpressure ventilation system to evacuate propellant fumes. In tanks like the T-72, the overpressure blower of the ventilator is automatically turned when the machine gun is fired, and the excess pressure inside the crew compartment creates a draft through the barrel of the PKT, which primarily helps to control the ingress of fumes, but may have some positive effect on barrel cooling as well.
One negative design trait of the PK family in terms of heat endurance is the use of a rotating bolt locking mechanism, owing to the fact that the locking lugs of the bolt engage into recesses on the trunnion directly behind the barrel. During intensive fire, carbon deposits build up much more rapidly on these locking recesses compared to the locking surfaces of other types of locking mechanisms, such as shoulders built into the receiver wall like in the SG-43 or in Degtyarev flapper-locked guns, and the receiver floor plate or crossbar in tilting lever guns (BAR, FN MAG, FN FAL) and in tilting bolt guns (LK vz. 26). Although the bolt face itself is not intensely polluted, the carbon build-up may cause bolt jamming issues, requiring either an adjustment of the gas regulator or emergency cleaning of the locking recesses.
The barrel of the PK is rated for 500 shots fired continuously in bursts at the practical rate of fire of 250 rounds per minute before a barrel change is mandatory. After 1,000 rounds of continuous fire in this fashion, the entire machine gun must be left to cool. A manual on the operation of the PK family of machine guns defines a short burst as lasting for 10 rounds and a long burst as lasting for 30 rounds. This is practically the same as the 20 or 30-shot burst lengths specified for other machine guns in foreign armies.
The thicker and longer barrel of the PKT retained the same heat limit of 500 shots fired continuously in bursts. Because the PKT is fed with 250-round boxes, this is equivalent to a continuous burst fire limit of two ammunition boxes before firing must halt in order to avoid premature wear of the barrel and prevent a drop in accuracy from overheating. This is good performance for a coaxial machine gun and it is particularly good when compared to weapons like the MG3, but it is principally the same as heavier machine guns like the FN MAG. The MAG 60-40 and M240 have a 2.49 kg barrel, unified with the MAG 58 infantry variant except in the lack of a front sight, and for these guns, a barrel change is required after 10 minutes of fire at the nominal sustained rate (100 RPM) or after 2 minutes of fire at the nominal rapid rate (200 RPM), equivalent to 400 shots fired continuously in bursts. The M60 machine gun also had a heat limit of 400 shots fired continuously in bursts at the same nominal rapid fire rate of 200 RPM. Such a direct comparison may not be completely valid due to possible differences in the criteria for the heat limit, but broadly speaking, this serves as a reasonable indicator of the heat limits of these machine guns.
AMMUNITION
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| 1,2 - LPS light ball from different years of manufacture, 3,4 - T-46 tracer, 5,6 - B-32 armour-piercing incendiary |
On all Soviet tanks from the T-55A to the T-80U and in modern Russian tanks like the T-90A, the PKT or PKTM would be fed with 250-round boxes of belted ammunition linked in 50-round segments. Each 250-round box weighs 9.4 kg fully loaded.
The standard combat load of 7.62mm ammunition was 2,000 rounds for most Soviet AFVs. Proprietary high capacity boxes did not exist for the machine guns of any Soviet armoured vehicle until the advent of the BMP-1 which had a special 2,000-round container for its coaxial machine gun.
The practice of using standard large capacity ammunition boxes for the coaxial machine gun dates back to the invention of the triple-stack 63-round pan magazine for mounted DP machine guns in 1928 and its subsequent use in DT and DTM machine guns in Soviet tanks to facilitate longer sustained fire. When the DTM was replaced by the SGMT medium machine gun, it was fed with 250-round boxes that were also standard for wheeled and tripod-mounted SG-43 machine guns. This did not change when the Soviet Army transitioned to the PK series, as the 250-round boxes for the PKT were also standard for tripod-mounted PKS machine guns and for PKB machine guns on armoured personnel carriers.
In the Soviet Army, the three primary ammunition types used in PKT machine guns were:
The three bullets are shown in the drawing below in this order, from left to right.
The components are:
All of the cartridges had steel cases. The use of steel for the cartridge cases instead of brass was a strategic decision that was related to the expense and availability of the two materials.
Usually, a mixture of all three ammunition types are linked into standard ammunition boxes. A typical belt would be sorted into groups of three, each group having two non-tracer rounds and one tracer round (2:1 ratio). The order of bullet types would be as follows.
For comparison, a typical mixture for M73 machine guns is Ball to Tracer rounds in a 3:1 ratio and the preferred mixture for M240 machine guns is Ball to Tracer in a 4:1 ratio. The higher concentration of bullets with an incendiary payload in a standard Soviet belt permits easier fire correction at long range, not to mention that it also slightly enhances the destructive effect on the target by increasing the probability of starting a fire.
The practice of using standard large capacity ammunition boxes for the coaxial machine gun dates back to the invention of the triple-stack 63-round pan magazine for mounted DP machine guns in 1928 and its subsequent use in DT and DTM machine guns in Soviet tanks to facilitate longer sustained fire. When the DTM was replaced by the SGMT medium machine gun, it was fed with 250-round boxes that were also standard for wheeled and tripod-mounted SG-43 machine guns. This did not change when the Soviet Army transitioned to the PK series, as the 250-round boxes for the PKT were also standard for tripod-mounted PKS machine guns and for PKB machine guns on armoured personnel carriers.
In the Soviet Army, the three primary ammunition types used in PKT machine guns were:
- 57-N-323S light ball round with LPS bullet
- 7BZ-3 API (armour-piercing incendiary) round with B-32 bullet
- 7T2 API-T (armour-piercing incendiary tracer) round with T-46 bullet
The three bullets are shown in the drawing below in this order, from left to right.
The components are:
- Tombak-clad steel jacket
- Lead-antimony alloy
- Steel core
- Tracer cup
- Tracer element
- Incendiary charge
All of the cartridges had steel cases. The use of steel for the cartridge cases instead of brass was a strategic decision that was related to the expense and availability of the two materials.
Usually, a mixture of all three ammunition types are linked into standard ammunition boxes. A typical belt would be sorted into groups of three, each group having two non-tracer rounds and one tracer round (2:1 ratio). The order of bullet types would be as follows.
Ball - Ball - T - Ball - Ball - T - Ball - AP-I - T
For comparison, a typical mixture for M73 machine guns is Ball to Tracer rounds in a 3:1 ratio and the preferred mixture for M240 machine guns is Ball to Tracer in a 4:1 ratio. The higher concentration of bullets with an incendiary payload in a standard Soviet belt permits easier fire correction at long range, not to mention that it also slightly enhances the destructive effect on the target by increasing the probability of starting a fire.
It is worth noting that the belt composition for an infantry PK or PKM would consist of 3 or 4 ball rounds to 1 tracer or AP-I round. There was no fixed rule on how a belt should be ordered, but officially, a ratio of 1 tracer to 3 ball was specified. Compared to these infantry machine guns, a PKT or PKTM would have a much higher concentration of ammunition with firestarting potential, and a much shorter interval of tracers for fire correction, supplemented by the higher fire rate, which increases the density of tracers rounds for a given burst time.
Overall, 7.62x54mm ammunition ballistically outperformed 7.62x51mm ammunition to an extent, but remained firmly within the same performance class with little to no practical difference in performance. However, it is worth noting that 7.62x54mm ammunition operates at a lower pressure than .30-06 and 7.62x51mm ammunition, which is reflected in its lower muzzle velocity for a given barrel length. For the same or comparable muzzle velocity, 7.62x54mm ammunition requires a 720 mm (28.3") barrel whereas .30-06 or 7.62x51mm requires only a 610mm (24") barrel.
Overall, 7.62x54mm ammunition ballistically outperformed 7.62x51mm ammunition to an extent, but remained firmly within the same performance class with little to no practical difference in performance. However, it is worth noting that 7.62x54mm ammunition operates at a lower pressure than .30-06 and 7.62x51mm ammunition, which is reflected in its lower muzzle velocity for a given barrel length. For the same or comparable muzzle velocity, 7.62x54mm ammunition requires a 720 mm (28.3") barrel whereas .30-06 or 7.62x51mm requires only a 610mm (24") barrel.
LPS (Ball)
The LPS bullet is a light ball bullet with a mild steel core. The bullet has a weight of 9.6 g and has a muzzle velocity of 855 m/s when fired from the PKT. Between the steel core and the jacket is a lead filler. Its purpose is to help seat the core, but it also functions as additional mass at the circumference of the bullet which increases the rotational inertia of the bullet. This allows the bullet to remain spinning at a sufficient rate to remain stable at longer distances than would be otherwise possible without the lead filler.
The LPS entered service in the Soviet Army in 1953 as a universal ball bullet for rifles and machine guns. At the same time, the production of ammunition with L bullets (light ball with lead core) and D bullets (heavy ball with lead core) was discontinued. The standardization of bullets had a significant economic effect as it allowed Soviet ammunition production facilities to be optimized for a single product, and the shift to a new ball bullet with a steel core also brought long-term cost savings by conserving lead.
Moreover, the LPS bullet had superb ballistic properties that allowed it fulfill the function of heavy ball bullets while having a bullet of the same weight as light ball bullets. The weight of the LPS bullet, 9.6 grams, was identical to the L obr. 1908/30 light ball bullet with a lead core which had a muzzle velocity of 855 m/s when fired from an SG-43 or SGM medium machine gun. The D obr. 1930 heavy ball bullet weighed 11.8 grams and had a muzzle velocity of 800 m/s when fired from an SG-43 or SGM. The maximum range of the L bullet was 3,800 meters whereas the D bullet achieved a maximum range of 5,000 meters, matching the .30 cal M1 ball round, which weighed 11.3 grams and had a muzzle velocity of 807 m/s when fired from a 24" barrel. The maximum range of the LPS bullet when fired from an SG-43, SGM, or PKT at a nominal muzzle velocity of 855 m/s is 4,600 meters.
The L bullet produced less recoil, and was best suited for short to medium range direct fire from light machine guns and infantry rifles. The D bullet was optimized for long range fire from medium or heavy machine guns against area targets using indirect fire techniques. It also provided better long range direct fire performance in terms of dispersion and lethality. However, the role of heavy bullets was deemed obsolete when actual combat experience during the early stages of the so-called Great Patriotic war showed that long range fire from machine guns was a waste of ammunition which was only exacerbated if indirect fire was used.
Nevertheless, light and heavy bullets were still issued for rifles, DP light machine guns and SG-43 medium machine guns respectively with the expectation of fulfilling their theoretical roles during the war. This practice continued into the immediate postwar period, most notably for tanks, which had sights marked for heavy bullets out to a range of 2,000 meters. For engagements at less than a kilometer, the distinction between L and D bullets is negligible, and remains marginal even at 1,200 meters. This is clearly visible in the sights below, the one on the left belonging to the serial SG-43 and the one on the right being an experimental sight made by Mikhail Kalashnikov as a proposed upgrade to the SG-43. The appearance of the LPS bullet made the distinction between light and heavy bullets effectively redundant even for long range fire, although it did not correspond exactly to either the L or D bullets, so special attention must be paid to range conversions for older machine guns with long range leaf sights marked for both.
In the Cold War context, the main implication of the switch to the LPS bullet was the unification in supply and machine gun sights, as all ammunition (Ball, AP-I, Tracer) now shared effectively identical ballistics, and for light machine guns and rifles previously firing L bullets, LPS had the additional benefit of providing improved lethality at longer range by retaining more kinetic energy and having the ability to readily penetrate helmets and light cover. Infantry rifles did not require the shooter to apply range conversions to the sight, because the ballistic trajectory of LPS bullets was effectively the same as L bullets at short range. Due to the large quantities of L and D ammunition stockpiled, they remained in service well after 1953 but were relegated to use in training. By the time the PKT replaced the SGMT in the Soviet Army, LPS ammunition had been firmly established as the new standard. The production of cartridges with LPS bullets was discontinued in 1988.
Relative to other bullets of its class, the LPS design is not particularly heavy, despite its good energy retention at long range. The weight of the LPS bullet is identical to the 7.62x51mm M80 ball bullet, which has a nominal weight of 147 grains (9.52 grams) but can weigh up to 9.66 grams (149 grains). The M80 bullet is a bimetallic bullet with a cupronickel jacket and a lead core, and is 24.2mm long. Because the core of the LPS bullet is made of steel, which is less dense than lead, the bullet had to be significantly longer (32.25mm) to be of a similar weight, and by a combination of its greater elongation and a streamlined shape with a boattail, the LPS bullet has a superior ballistic coefficient compared to the M80 bullet. The M80 bullet is a flat based bullet like the L bullet, and has a similar maximum range of 3,930 meters when fired at a nominal muzzle velocity of 856 m/s, which is almost 700 meters less than the LPS bullet. The M59 ball bullet which the M80 replaced had a mild steel core like the LPS bullet, but its ballistic coefficient was still almost identical to the M80 (to ensure retroactive interchangeability for sighting purposes), and as such, no noticeable improvement in the flatness of the trajectory was gained. This is reflected by its maximum range of 3,820 meters when fired at a nominal muzzle velocity of 856 m/s.
Officially, the use of a mild steel core in the LPS bullet only negligibly improved its obstacle penetration performance compared to the L bullet obr. 1908/30, but it drastically increased the maximum range at which steel helmets could be pierced. The LPS ball round is rated to perforate a generic steel helmet (most likely SSh-40) at a range of 1,770 meters and it defeats generic body armour (most likely a flak vest) at a range of 1,200 meters. For comparison, the D obr. 1930 heavy bullet was rated to pierce a Soviet steel helmet at a distance of 1,400 meters, and the 7.62x51mm M80 ball round is only rated to penetrate one side of a U.S Army M1 steel helmet at 800 meters. At a distance of 1,000 meters, an LPS bullet will perforate a compacted snow bank with a thickness of 700-800mm or an earthen barrier with a thickness of 250-300mm. The bullet will also perforate a dry pine plank with a thickness of 200mm at a range of 1,200 meters. A brick wall with a thickness of 100-120mm is perforated at a distance of 200 meters.
The table below shows the thicknesses of RHA and 5083 aluminium that can be perforated by this bullet at a variety of ranges and slopes.
In the mid-1980's, it was determined that the proliferation of the new-generation PASGT personal protection equipment among NATO forces significantly reduced the effectiveness of existing ball cartridges with an LPS bullet. However, the impetus of this research project is not entirely clear given that the PASGT vest and helmet were only capable of stopping small shell fragments and were completely insufficient against ordinary LPS ball bullets at any meaningful range. Even the NATO standard M80 ball round with a lead core had no issues perforating the 13 plies of Kevlar that formed the vest. It is likely that comprehensive information on the characteristics of the PASGT kit was not available in the USSR at the time.
The new LPS bullet with a heat-treated steel core entered service in 1986. Its ballistic characteristics were identical to the older LPS bullet it replaced, and differed only in the increased armour penetration power.
The original B-32 bullet introduced into service in the year 1932 was an armour-piercing incendiary bullet with an incendiary pellet placed in a cavity in the nose of the bullet, ahead of the pointed steel core. An aluminium, magnesium and barium nitrate compound is used for the incendiary charge, which weighed 0.26 grams. The steel core, which weighs 5.38 grams, has a diameter of 6.09mm and a length of 30mm. The total length of the bullet is 36.83mm, and the total weight is 10.4 grams. Like the LPS bullet, the steel core is surrounded by a lead filler. The closest foreign counterpart to the B-32 bullet is the .30-06 caliber AP M2 bullet, which weighs 10.8 grams, has a total length of 35.3mm and has a steel core with a diameter of 6.17mm and a length of 27.4mm.
The table below shows the thicknesses of RHA and 5083 aluminium that can be perforated by this bullet at a variety of ranges and slopes.
As the table shows, the penetration of the B-32 bullet into RHA steel reaches 0.7 inches (17.78mm) at 0 degrees at its muzzle velocity of 855 m/s when fired from a PKT. For comparison, the .30-06 caliber AP M2 bullet perforates 0.68 inches (17.27mm) of RHA steel at 0 degrees at its muzzle velocity of 845 m/s when fired out of an M1919 or M37. A direct comparison between these two bullets is valid because both were evaluated by the U.S military under the Navy Criterion.
In 1954, the Soviet Army adopted the B-32M armor-piercing incendiary bullet to replace the B-32 bullet mod. 1932. The new design was distributed under the same old name of B-32, but for the sake of clarity, it will hereby be referred to as B-32M. The main difference of the new B-32M bullet was an additional incendiary charge placed behind the steel core to supplement the incendiary charge in the nose of the bullet. The presence of an incendiary charge behind the steel core drastically increases the incendiary effect produced behind an armour plate perforated by the bullet.
The weight of the B-32M bullet is 10.37 grams. The difference in weight from the original B-32 is insignificant and the ballistics of the new bullet remained identical.
The T-46 tracer bullet is designed purely for fire correction purposes. It was initially intended to accompany L ball bullets, but continued to be used with LPS ball. A large tracer element dominates the majority of the volume in the bullet, leaving only a small lead filler in the tip. The bullet weighs 9.6 grams and has a lower muzzle velocity than LPS. The exact muzzle velocity when fired from a PKT is unknown.
When fired, the combustion of the propellant powder charge ignites the tracer composition which burns during the flight of the bullet, giving a bright luminous trail, clearly visible during day and night. The bullet head is painted green. However, contrary to a persistent myth related to the green colour code on the bullet, the tracer colour itself is not green but red. The older T-30 tracer bullet, which the T-46 replaced, had a colour that was officially white and was actually white with a greenish tinge.
The bullet tracer is guaranteed to burn to a distance of 1,000 meters. This was an improvement over the T-30, which provided a trace only up to a distance of 800 meters. The tracing period is up to 3 seconds, which nominally allows the bullet to form a visible trace beyond 1,000 meters, but reliable tracing is not provided beyond 1,000 m due to a variety of factors.
Relative to other bullets of its class, the LPS design is not particularly heavy, despite its good energy retention at long range. The weight of the LPS bullet is identical to the 7.62x51mm M80 ball bullet, which has a nominal weight of 147 grains (9.52 grams) but can weigh up to 9.66 grams (149 grains). The M80 bullet is a bimetallic bullet with a cupronickel jacket and a lead core, and is 24.2mm long. Because the core of the LPS bullet is made of steel, which is less dense than lead, the bullet had to be significantly longer (32.25mm) to be of a similar weight, and by a combination of its greater elongation and a streamlined shape with a boattail, the LPS bullet has a superior ballistic coefficient compared to the M80 bullet. The M80 bullet is a flat based bullet like the L bullet, and has a similar maximum range of 3,930 meters when fired at a nominal muzzle velocity of 856 m/s, which is almost 700 meters less than the LPS bullet. The M59 ball bullet which the M80 replaced had a mild steel core like the LPS bullet, but its ballistic coefficient was still almost identical to the M80 (to ensure retroactive interchangeability for sighting purposes), and as such, no noticeable improvement in the flatness of the trajectory was gained. This is reflected by its maximum range of 3,820 meters when fired at a nominal muzzle velocity of 856 m/s.
Officially, the use of a mild steel core in the LPS bullet only negligibly improved its obstacle penetration performance compared to the L bullet obr. 1908/30, but it drastically increased the maximum range at which steel helmets could be pierced. The LPS ball round is rated to perforate a generic steel helmet (most likely SSh-40) at a range of 1,770 meters and it defeats generic body armour (most likely a flak vest) at a range of 1,200 meters. For comparison, the D obr. 1930 heavy bullet was rated to pierce a Soviet steel helmet at a distance of 1,400 meters, and the 7.62x51mm M80 ball round is only rated to penetrate one side of a U.S Army M1 steel helmet at 800 meters. At a distance of 1,000 meters, an LPS bullet will perforate a compacted snow bank with a thickness of 700-800mm or an earthen barrier with a thickness of 250-300mm. The bullet will also perforate a dry pine plank with a thickness of 200mm at a range of 1,200 meters. A brick wall with a thickness of 100-120mm is perforated at a distance of 200 meters.
The table below shows the thicknesses of RHA and 5083 aluminium that can be perforated by this bullet at a variety of ranges and slopes.
In the mid-1980's, it was determined that the proliferation of the new-generation PASGT personal protection equipment among NATO forces significantly reduced the effectiveness of existing ball cartridges with an LPS bullet. However, the impetus of this research project is not entirely clear given that the PASGT vest and helmet were only capable of stopping small shell fragments and were completely insufficient against ordinary LPS ball bullets at any meaningful range. Even the NATO standard M80 ball round with a lead core had no issues perforating the 13 plies of Kevlar that formed the vest. It is likely that comprehensive information on the characteristics of the PASGT kit was not available in the USSR at the time.
The new LPS bullet with a heat-treated steel core entered service in 1986. Its ballistic characteristics were identical to the older LPS bullet it replaced, and differed only in the increased armour penetration power.
B-32 (AP-I)
The original B-32 bullet introduced into service in the year 1932 was an armour-piercing incendiary bullet with an incendiary pellet placed in a cavity in the nose of the bullet, ahead of the pointed steel core. An aluminium, magnesium and barium nitrate compound is used for the incendiary charge, which weighed 0.26 grams. The steel core, which weighs 5.38 grams, has a diameter of 6.09mm and a length of 30mm. The total length of the bullet is 36.83mm, and the total weight is 10.4 grams. Like the LPS bullet, the steel core is surrounded by a lead filler. The closest foreign counterpart to the B-32 bullet is the .30-06 caliber AP M2 bullet, which weighs 10.8 grams, has a total length of 35.3mm and has a steel core with a diameter of 6.17mm and a length of 27.4mm.
The table below shows the thicknesses of RHA and 5083 aluminium that can be perforated by this bullet at a variety of ranges and slopes.
As the table shows, the penetration of the B-32 bullet into RHA steel reaches 0.7 inches (17.78mm) at 0 degrees at its muzzle velocity of 855 m/s when fired from a PKT. For comparison, the .30-06 caliber AP M2 bullet perforates 0.68 inches (17.27mm) of RHA steel at 0 degrees at its muzzle velocity of 845 m/s when fired out of an M1919 or M37. A direct comparison between these two bullets is valid because both were evaluated by the U.S military under the Navy Criterion.
In 1954, the Soviet Army adopted the B-32M armor-piercing incendiary bullet to replace the B-32 bullet mod. 1932. The new design was distributed under the same old name of B-32, but for the sake of clarity, it will hereby be referred to as B-32M. The main difference of the new B-32M bullet was an additional incendiary charge placed behind the steel core to supplement the incendiary charge in the nose of the bullet. The presence of an incendiary charge behind the steel core drastically increases the incendiary effect produced behind an armour plate perforated by the bullet.
The weight of the B-32M bullet is 10.37 grams. The difference in weight from the original B-32 is insignificant and the ballistics of the new bullet remained identical.
T-46 (T)
The T-46 tracer bullet is designed purely for fire correction purposes. It was initially intended to accompany L ball bullets, but continued to be used with LPS ball. A large tracer element dominates the majority of the volume in the bullet, leaving only a small lead filler in the tip. The bullet weighs 9.6 grams and has a lower muzzle velocity than LPS. The exact muzzle velocity when fired from a PKT is unknown.
When fired, the combustion of the propellant powder charge ignites the tracer composition which burns during the flight of the bullet, giving a bright luminous trail, clearly visible during day and night. The bullet head is painted green. However, contrary to a persistent myth related to the green colour code on the bullet, the tracer colour itself is not green but red. The older T-30 tracer bullet, which the T-46 replaced, had a colour that was officially white and was actually white with a greenish tinge.
The bullet tracer is guaranteed to burn to a distance of 1,000 meters. This was an improvement over the T-30, which provided a trace only up to a distance of 800 meters. The tracing period is up to 3 seconds, which nominally allows the bullet to form a visible trace beyond 1,000 meters, but reliable tracing is not provided beyond 1,000 m due to a variety of factors.
While burning, the tracer flare interacts with the flow of air at the tail of the bullet, filling the low-pressure zone to allow more of the flow to merge rather than form a turbulent wake, thus reducing the tail drag to some extent. The resulting reduction in drag, together with a streamlined form, allowed the T-46 bullet to maintain a trajectory similar to an LPS bullet despite the gradual burn-off of the bullet mass, and therefore, the loss of sectional density. Immediately after its exit from the muzzle, the T-46 bullet tends to undershoot LPS bullets due to its slightly lower muzzle velocity. This is compensated out to 1,000 meters by the lower drag of the T-46 bullet, but gunners need to be aware that the fall of a burst may be below the impact of the tracers, especially at closer ranges. As the tracer element eventually burns out near the end of its tracing period, the divergence of the bullet trajectory relative to LPS reverses. Incidentally, it is worth noting that due to inherent variations in tracer weights due to factory filling margins, the tracing period and intensity can vary slightly, with a corresponding variation in the effect on the streamlining of the bullet. This worsens its dispersion compared to ball and AP-I bullets.
In 1969, work began on the modernization of the T-46 bullet. The new model was designated T-46M and adopted in 1974. The lead filler was enlarged and the size of the tracer element was downsized, and the overall weight of the bullet decreased to 9.4 grams. The same tracing range was maintained by switching to a slower-burning tracer compound, thus achieving the same burn time of 3 seconds. The tracer colour remained red. Moreover, the tracer had a delayed ignition so that it only began to burn after travelling 80-120 meters downrange of the muzzle. This helped the firing position of the machine gun to remain concealed. The new bullet matched the ballistic trajectory of LPS bullets more closely.
In 1969, work began on the modernization of the T-46 bullet. The new model was designated T-46M and adopted in 1974. The lead filler was enlarged and the size of the tracer element was downsized, and the overall weight of the bullet decreased to 9.4 grams. The same tracing range was maintained by switching to a slower-burning tracer compound, thus achieving the same burn time of 3 seconds. The tracer colour remained red. Moreover, the tracer had a delayed ignition so that it only began to burn after travelling 80-120 meters downrange of the muzzle. This helped the firing position of the machine gun to remain concealed. The new bullet matched the ballistic trajectory of LPS bullets more closely.
Very simple in construction , more primitive than AK . Without mechanical components trigger - cock units
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