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| As required, the operator provides fire support by shooting the PKM Kalashnikov Modernized Machinegun. |
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Text by Janne Pohjoispaa
Likely inspired by the German MG34 and MG42 general purpose machine guns they encountered during WWII, Soviet designers started to develop their own version of a portable, belt-fed multi purpose machine gun after the Second World War.
While many attempts were made to replace aging Maxims since the 1930's, no satisfactory design had been found. A brainchild of Vasily Degtyarev, the DS-39 was issued to the Red Army just before the WWII, in 1939. It was quickly discovered that the DS-39 had an improperly engineered belt feed mechanism which damaged the cartridge cases while stripping them off from the belt. Tested in the Finnish-Russo Winter War (1939-1940), the DS-39 was found too complicated and liable to malfunctions especially in cold and dusty conditions. The DS-39 was soon withdrew from service.
Next step was the SG-43 (followed later by an improved variation known as the SGM) designed by Petr and Mikhail Goryunov. Goryunov's machine gun was far more reliable than DS-39 and lighter than the old Maxims. Mounted on a wheeled carriage or tripod it served well in the medium MG role, and was converted into a coaxial MG as the SGTM. For infantry the SG43/SGM was just a medium machine gun like the DS-39 or Maxim, however, shortly after WWII, a belt fed version of Degtyarev's DPM light machine gun, the RP-46 was adopted as 'the company machine gun'. The RP-46 was lighter and more manoeuvrable than its belt fed predecessors, but poorly suited in roles other than as a light machine gun.
The RPD light machine gun firing an intermediate 7.62 x 39 mm M43 round
was considered for the GPMG role. The 7.62 x 39 mm M43 caliber cartridge was
already standardised for the
AK-47 assault rifles
and SKS semi-automatic
carbines. One caliber for all infantry small arms would have been an ideal
situation, but the 7.62 mm M43 seriously lacked both the penetration and
effective range needed in a GPMG. It was dropped and interests were turned
for developing a whole new GPMG, firing more potent the 7.62 x 54 R caliber
round.
In the early 1950's, two Soviet designers, Grigory Nikitin and Yuri Sokolov started to design a belt fed machine gun chambered for the 7.62 mm rimmed round, while the renowned Mikhail Kalashnikov worked with his own design. The both Nikitin-Sokolov and Kalashnikov weapons were gas operated having rotating bolts and quite similar external appearance. Tests arranged in 1960 revealed that Kalashnikov's design, the PK (Pulemyot Kalashnikova) was more reliable. The PK was also less expensive to manufacture, and it was selected over the Nikitin-Sokolov design. The time for Nikitin and Sokolov would come ten years later. In 1972 the 12.7 x 108 mm NSV heavy machine gun designed by Nikitin, Sokolov and Vladimir Volkov was adopted to replace the DshK and DShKM heavy machine guns - but that is another story.
In 1961 Kalashnikov-designed PK-series was adopted as the standard GPMG
of the Red Army. Eight years later, in 1969 a product improved version
called the
PKM (Pulemyot Kalashnikova Modernizirovanniy)
was introduced. The
PKM can be easily recognised for its lighter, unfluted barrel and a hinged
shoulder strap on the buttstock. The PK/PKM series has changed into four
configurations:
General purpose machine guns chambered for the 7.62 mm rimmed cartridge are
quite scarce. However, In addition to those mentioned below, there exists
(or have existed) a few other GPMG's chambered for the 7.62 x 54 R
cartridge. Czechoslovakia didn't adopted a Soviet machine gun, but fielded
the VZ 59 GPMG of their own design. The VZ 59, also produced in the 7.62 mm
NATO caliber has not been distributed widely outside the borders of former
Czechoslovakia. During WWII, famous Finnish arms designer Aimo J. Lahti
designed the L-41 "Sampo" general purpose machine gun chambered for the 7.62
x 54 R round, which was used by Finnish Army in a limited capacity during
the Second World War. The L-41 didn't stay in service after the war. In
addition to this, there was the 7.62 x 54 R caliber variation of German MG42
developed and built in Finland. The 7.62 x 54 R caliber MG42 never went
beyond the prototype stage.
During the Cold War, the PK-series machine guns were widely distributed all over the world and fired in anger in many conflicts. PK-series machine guns have been manufactured or are still in production at least in former Soviet Union/Russia, Bulgaria, Hungary, Rumania, mainland China (Type 80, export only), Yugoslavia (M84) and probably in Poland and former East Germany.
Like all other true machine guns, the PK fires from an open bolt. Despite
that, the basic operating principle follows the familiar Kalashnikov
pattern. The PK has a rotating bolt type with two locking lugs, similar to
the AK bolt. The PK's bolt larger and more robust; it has larger face to
accept a 7.62 mm rimmed round and a single claw extractor similar to the AK
assault rifles.
Because the PK fires from an open bolt, the firing pin is temporarily fixed
on the bolt carrier. The firing pin can be removed with the bolt, but while
the bolt is rotating along its carrier guideway, the firing pin stays locked
on the bolt carrier. It will project and strike a primer while the bolt
rotates to engage on the locking lugs. The PK's bolt carrier is somewhat
similar to the AK slide, except it is turned upside down, it is bigger,
heavier and has a less complex shape. The PK is gas operating with a long
stroke piston i.e. the gas piston is permanently mounted on the bolt carrier
and moves with it. The gas piston and its rod are chrome-plated for better
corrosion resistant and pivoted on the bolt carrier. The hinge allows for
slight bending of the carrier/gas piston while it is removed/installed. Not
all PK series machine guns have a slide buffer, but Hungarian and
Yugoslavian made ones do. If you have examined buffers in other machine
guns, the buffer may be a fancy name for 1/4 inch thick plate of
fiber-reinforced reddish plastic placed at rear end of the recoil spring
guide. However, it will reduce recoil by preventing a straight contact
between bolt carrier and the receiver, and it also helps with removing and
installing the recoil spring guide. The PK family has the gas piston and
tube mounted beneath the barrel. The gas tube is fixed on the receiver by a
spring steel latch, and it can be separated for cleaning.
The gas block is mounted permanently mounted on the barrel, and
connected to the gas tube via the gas regulator. The infantry versions have
an exhaust type, three-position regulator. Position "1" is a basic setting,
which is used with clean gun, and next steps "2" and "3" are used while
action gets more dirty. The gas regulator can be adjusted by using a
cartridge or empty case as tool. Theoretical cyclic rate is 650 rpm,
according Russian literature. Because the PK action has no proper buffering
device, which is required for higher cyclic rates, increasing the cyclic
rate with regulator settings is not recommended, because it increases the
wear of the receiver and operating parts, and will reduce service life of
the gun. The PKT and PKB type machine gun have a different "Venturi" type
gas regulator, which doesn't exhaust fumes to the vehicle interior.
The receiver is a U-section stamped from 1.5 mm sheet steel and assembled
by rivetings and spot weldings. The receiver has double walls made from two
1.5 mm plates welded one upon another. The receiver top cover is stamped
from sheet steel and hinged at front to the receiver and locked at the back
with a spring loaded latch. The ejector is similar to the AK's and riveted
inside the receiver. The PK ejects empty cases through the ejection port
located at left side on receiver. The ejection port has a spring-loaded dust
cover. With proper gas selector setting, the ejection cycle is not as
violent as the AK cycle and the PK won't damage ejected cases. The PK expels
empty cases straight to left at a distance of about 1 m.
The barrel extension is riveted on the front of the receiver in the AKM manner. The barrel extension mounts the gas piston tube and includes the quick-change barrel locking mechanism borrowed from the SG43/SGM machine gun. The barrel extension has a straight boring to accept a cylinderical mounting piece of barrel, and two indexing studs to keep the barrel in right position. A horizontally sliding locking latch fixes barrel to the receiver.
The barrel is the easiest way to distinguish the PK and its modernized
variation, the PKM. The PK has heavier, fluted barrel, while the PKM barrel
is lighter (it weighs 2.35 kg and has no longitudinal grooves). The armored
vehicle variations PKT/PKTM and PKB/PKBM have even heavier barrels, better
suited to the sustained fire role. Like most other small arms of Com-Bloc
origin, the PK family barrels have chrome-plated bores and chambers. The PKM
bore has four grooves with a right-hand twist of one turn in 225 mm. The
barrel length is 602 mm, which doesn't include the flash hider or any other
muzzle device. The muzzle has a left-hand metric M18 x 1.5 thread to mount a
flash hider or a blank firing adapter. There is an AK-type spring-loaded
plunger to hold the muzzle device in correct position. There exists at least
two different PK-series flash hiders. Earlier and most common type is
similar to the M14 flash hider with five longitudinal slots. More recent
model is shorter and conical, also having five slots. Barrel have a pivoted
handle, which can be used as the lever to crank the barrel out from its
housing.
The trigger housing is mounted permanently underneath the receiver, and it includes the trigger guard. Trigger mechanism, very similar to the RPD is simple, and also very similar to many submachine guns firing from an open bolt. The rotating safety catch located on the left side of trigger housing has two settings: Safe and full-auto. There in no provision for semi-automatic fire, which is, after all, generally considered useless in general purpose machine guns.
The PK/PKM machine guns will usually appear with a skeletonized buttstock made from laminated wood. However, there is no rule without a few exceptions: Some examples of Bulgarian-made PK machine guns have appeared with plastic buttstocks, Chinese Type 80 has skeletonized buttstock, but made from solid wood, and Yugo M84 has also a solid wood buttstock. The PK and PKM have steel buttplates with a trapdoor compartment for cleaning gear. The PKM has a steel shoulder strap. Integral oiler is located in the buttstock. Pistol grip and barrel handle grip plates are usually made from reddish, bakelite type plastic material.
Like most other small arms of Soviet and Warsaw Pact origin, the PK series machine guns will usually feature a black baked enamel finish. Some other examples have a blued or manganese phosphate (parkerized) finish.
The belt fed machine gun firing a rimmed ammunition has a more complicated feeding mechanism than a counterpart chambered for a rimless cartridge. Russians/Soviets have used rimmed 7.62 x 54 R cartridge for more than 100 years, so they have a lot of experience of designing belt-fed mechanisms for rimmed cartridges. Russian designed belt-fed ground machine guns, chambered for the 7.62 mm rimmed round include Degtyarev-designed worthless DS-39, the RP-46 based on a magazine feed DPM light machine gun, Goryunov-designed SG-43 and SGM to name only those entered in service. There was also a series of fast firing, belt fed ShKAS (Shpitalniy - Komaritsky) aircraft machine guns with 1800 rpm rate of fire.
The PK series belt-fed mechanism, which is located over the breech block includes some similarities to the RP-46 and Goryunov designs. The double hooked cartridge gripper is similar to one used in SG 43 and SGM machine guns. Also double receiver covers, the feed cover which includes the feed tray and the top cover, are similar to the Goryunov's. The spring-loaded depressing arm is a take-off from the RP-46.
The PK family utilizes non-disintegrating, closed pocket metallic belt. Actually it is the same as used with the Soviet Maxims, the RP-46 and SG43/SGM machine guns. The PK belts will usually appear in three lengths; for 100, 200 or 250 rounds. The 100 round belt is used with small belt box that can be snapped beneath the receiver. In light machine gun configuration, the 100 rd belt with that assault box is usually employed. The 200 rd and 250 rd belts will fit in bigger belt box, which is the same as is used with the Goryunovs. The 250 rd belt box is a logical choice if fired from the tripod, and it can be readily mounted on the tripod. Both Russian belt boxes are stamped from sheet aluminium. The 250 rd type is all aluminium, while the 100 rd box has an aluminium frame with a steel cover. Both types have canvas carry handles.
The "pull-off" type belts are usually used with machine guns chambered for rimmed rounds, but that is not the only way to go. The most ingenious feeding system for rimmed rounds that I have seen was designed during the WWII by Aarno Lahti of Finland, brother of famous small arms designer Aimo J. Lahti, for the 7.62 x 54 R caliber version of the MG42. The 7.62 x 54R caliber MG42 used a "push-through" type belt, which allowed the use of a standard MG42 fed mechanism. Few prototypes were converted from German-made guns, but license-production never started. The 7.62 x 54 R caliber MG42 left as a technical curiosity.
The PK series belt fed mechanism works as follows: The belt comes to the feed tray from the right side of the PK. The feed tray is located over the chamber, and cartridges are pulled out from the belt to rearwards. While the bolt carrier starts withdraw after a shot is fired, the cartridge gripper pulls the next cartridge from the belt, and bolt carrier movement activates the feed pawl to move leftwards to pull the belt inwards. After travelling about 9 cm backwards the cartridge stops at the feed cam mounted on the top cover, and is dropped over the feed lips of the feed tray by a spring-loaded depressing arm. Just before that the ejector expels an empty case through a spring loaded ejection port on left side of receiver. Bolt carrier continues its withdraw for about 4 cm. When the forward motion begins, the bolt pushes the fresh round towards the chamber, and bolt carrier movement forces the feed pawl to move back to the right. A holding pawl located on the top cover retains the belt.
The PK series machine guns (except a coaxial version PKT, which has no sights) have fully adjustable iron sights. The front sight is similar to the AK assault rifles. Post-type front has curved protective ears, and like the AK's front sight, the PKM front sight is adjustable for both windage and elevation. The tangent-type rear sight has an open, U-shaped notch, and it is similar to ones used with the RPD SAW and RPK LMG, and it is adjustable for both windage and elevation. The PKM rear sight is graduated from 100 m to 1500 m with 100 m increments and 300 m battle sight setting. The sight picture is identical to the AK assault rifles and RPK light machine guns.
Our test specimen has no provision for mounting an optical sighting device, but recent PKM GPMGs will accept the four power 1P29 daytime sight (a copy of British SUIT) or the second-generation 1PN51 passive night sight. The scope mounting rail is located on the left side of receiver.
The PK and its modernized version are issued with a folding bipod, which is mounted on the gas tube. The bipod non-adjustable legs are stamped from sheet steel, and it is somehow similar to the RPK bipod. The bipod stays automatically in it's firing position by use of a spring-loaded hinge. While folded, the legs are kept together by a stamped hook. The three-piece cleaning rod is stored on the bipod right leg.
The PK machine gun was originally introduced in 1961 with a tripod designed by Evgeniy Samozhenkov. Samozhenkov's tripod weighed 7.7 kg, almost half less than the SGM tripod, and it still converted easily to both ground fire and anti-aircraft configurations. When the improved the PKM pattern was introduced in 1969, it was issued with a new and remarkably lighter tripod designed by Leonid Stepanov. The Stepanov mount can easily be described as a "light" tripod. Made almost entirely from steel stampings, it weighs only 4.5 kg. It has no buffering mechanism of any sort, and the cradle, which mounts the gun, is connected directly on traverse and elevation mechanism. The Stepanov light tripod can be easily modified ground fire role to AA-configuration.
Each tripod leg can be folded for transport or adjusted for proper height or finding an equilibrium in rugged terrain. While folded for transport, the tripod can be easily carried in field by one man. Like any other tripod, the Stepanov light tripod requires sandbags for maximum stability.
The Stepanov tripod issued with our test gun was manufactured in Kovrov (marked with an arrow inside oval ring) in 1977. It appeared to be unused. Tripod was clean and dry; apparently stored 20 years ago by wrapping it in paper treaded with corrosion inhibiting agent and putting it in a sealed container. During these years all lubricant have dried and frozen most moving parts. It required some muscles and lot of gun oil to get all hinged parts operate properly. Please note: If you are handling wrappings etc. Treated with Soviet/Warsaw Pact corrosion inhibiting agent, bear in mind that it is very poisonous.
In addition to the mounts described above, there exists a flexible vehicle mount, which accepts a standard PK or PKM.
In 1993 a new member of the PK family chambered for the unique 6 x 49 mm round was introduced. Called the Unified Machine Gun (UMG), it is basically similar to the PK/PKM, but has a shorter receiver, apparently with a simplified feed mechanism. The UMG has a longer barrel, while overall length (1150 mm) is approximately equal to the standard issue PK/PKM. This new Russian machine gun is relatively light in weight, as it weighs only 6.5 kg with a bipod. The revealed prototypes have no iron sights, but were fitted with an optical sighting device. In addition to the improved PK machine gun, the SVD based sniping rifle and AK assault rifle chambered for the 6 x 49 mm cartridge are also being developed.
Presumably inspired by the U.S. Army SAW research, the Soviets started developing the 6 mm ammunition primarily intended for infantry machine guns and sniping rifles in about 1980. The first type revealed was the 6 x 53 mm, which launched an 5.2 g bullet with a muzzle velocity of 1150 mps.
About ten years later the 6 x 49 mm cartridge was introduced. It has a rimless case with approximately the same rim diameter (11.4 mm) as a classic 7.62 x 39 mm round. The 6 x 49 mm round has muzzle velocity equal to the 6 x 53 mm, it is also extremely hot having higher chamber pressures than the 6 x 53 mm. While there is a risk for case separation, the case has a circular groove formed near the extractor groove to allow case stretching without risk of separation. For reliable operation, adequate headspace is critical in self-loading firearms. On the other hand, high pressure ammunition will require tight headspacing to be safe. Controlled case stretching as used with certain aircraft cannons allows use of workable headspacing, yet the gun is also safe to fire.
While not so prolific as Mikhail Kalashnikov's assault rifles, his belt fed general purpose machine gun is really an outstanding design. Not the least because it fires a complex rimmed round, but also because it is reliable, easily controllable and easy to operate. It will serve to the foreseeable future in existing forms or firing a new rimless cartridge, which might be a less complicated choice for belt fed weapons.
Note:
It is my special pleasure to introduce my Finnish colleague Janne
Pohjoispaa to a Russian reader.
The name of Pohjoispaa is known not only in his own country - Finland -
but also abroad. His works present a paragon of profound professional
analysis and knowledge of the subject under study. Behind the seemingly
typical Nordic cool style and discreet manner of presenting facts, we find a
sincere and hearty Pohjoispaa’s attitude to the subject that he loves - the
history of arms.
For Pohjoispaa, the history of arms is inseparable from the common human
values. Remaining a patriot of his country, he was able to rise above the
purely national problems and speak to the international audience about
entire periods of history, giving them his own individual interpretation.
The fact that the “Gun. Arms and Munitions” magazine offers its pages to
a very delicate issue that touches upon the complex episodes in the history
of Russo-Finnish relations, may be treated as a token of complete overcoming
by modern society the rather persistent after-war antipathies, if not
antagonisms.
I am sure, that the material on how the “Lahti-Saloranta 26” light
machine gun and its many variants were created, will be received by the
Russian lovers of the history of small arms with admiration and interest.
Valery N. Shilin,
Member of the Russian
Union of Journallists.
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