In 1964, the Soviet army adopted a light machine gun Kalashnikov RPK. This weapon was intended to replace the RPD machine guns, and one of the main goals of the project was to unify multiple types of weapons. The RPK was maximum commonality with the AKM assault rifle, which streamlined the production and operation. However, the PKK had several disadvantages. One of the main disadvantages of the design was the use of store-bought food instead of ammunition belts, which negatively impacted on the possible firepower and density of fire.
The original idea
In the late sixties started to develop new types of rifles and light machine guns under malinowsky cartridge 5,45 x39 mm. Seeing the challenges of new projects, in particular mixed store-bought food, the group of designers of the Izhevsk machine-building plant decided to study the possibility of creating a machine gun that combines all the advantages of different ways of feeding ammunition. In the fall of 1971, work began on the theme of “Poplin”. The main goal of this project was to develop a machine gun which would be about one and a half times higher than other samples.
Light machine gun RPK-74
In the works on creating a new machine gun was attended by several famous gunsmiths. Overall project management was carried out by Y. K. Alexandrov, who proposed some basic ideas and technical solutions. Also in development was attended by V. M. Kalashnikov and M. E. Dragunov (autumn 1972). In addition, a role in the development of the machine gun played head CB-3 A. I. Nesterov. For several years the team of designers managed to complete the task and create a weapon, devoid of shortcomings of existing systems. However, the development of a new project has been associated with many problems and difficulties.
Different ways of bunker machine guns have their advantages and disadvantages. So, the tape allows you to keep an intense fire for a long time without needing a recharge, but it has a lot of weight. Pie shops are much lighter and easier to operate, but have limited capacity. Thus, when a new weapon was necessary to determine which way the bunker is most fully meets the requirements.
The obvious, albeit difficult, way out of the situation was the simultaneous use of and ribbons, and shops. That was the essence of the theme of “Poplin”. Due to the proposed use of stores and feeds a sample of the new weapon received the designation PU (“a machine Gun with a unified filing”). Further to these letters was added a few times the figures are intended to refer to modifications of the weapon.
The creation of project documentation continued until 1973. At the same time all necessary drawings handed in the experimental shop of the plant. However, for various reasons, the Assembly pilot machine gun PU was delayed. Tests of a prototype of the new weapon was able to begin in the spring of 74. Such shifts of timing led to the fact that shortly after the beginning of testing at the factory had to start preparing for the subsequent verification of a machine gun in TSNIITOCHMASH.
The machine gun PU of the first model to use the ribbon cartridge and a detachable pie shops. Thus, the shooter can apply the most suitable and comfortable to the prospective application method of feeding ammunition. The tape was fed through a window in the left side of the receiver, and to install the shop used a window in its lower part.
The gun used cartridge 5,45 x39 mm and had gas automation on the basis of units and aggregates are borrowed from RPK-74. The machine gun was borrowed the barrel, bolt Assembly, fittings and other details. Receiver based on the nodes of the RPK-74, however, there were noticeable differences associated with the use of belt power. On the lateral surface and on the lid present extra punch to accommodate the desired units.
The design of the new weapon was unreliable. During the factory trials it was found that experienced gun can’t function after hitting into the water. If the inside of the receiver remained liquid, attempt to shoot could lead to the destruction of the locking mechanisms of the trunk.
To solve the problem of “hydrophobia” Y. K. Alexandrov suggested using a new bolt and new barrel. In addition, the updated version of the draft the breech was moved 1.5 mm forward. Indeed, this revision allowed us to get rid of negative consequences of the arms stay in the water. However, when testing the updated gun with a tape discovered a new problem. On average every third shot ended uticajem cartridge. It soon turned out that the reason for this was not entirely successful the layout of the nodes feeding ammunition. Receiver tape was located too far from the breech. Because of this, towards the cartridge chamber, the cartridge is held about 1.5 mm without support, because in this place there were no guides. After correcting this deficiency the number of uticany cartridge has decreased dramatically.
At the end of 1974 experienced gun PU passed for tests in TSNIITOCHMASH. The sample again showed their tendency to delay in shooting and also showed low reliability and survivability. At the beginning of the 75 trials were completed due to damage experienced with a machine gun. The next trial of fire ended with a broken rear part of the receiver.
Despite numerous challenges, testers TSNIITOCHMASH introduced a neutral report. It was noted that represented on the test, the product PU is not a full prototype, and is a technology demonstrator. Experienced gun showed the possibility of creating weapons with the combined system of supply of ammunition, but in its current form it required mass modifications.
During the first phase of the project “Poplin” were developed some variants of the systems of storage and supply of ammunition. Gun PU was proposed to equip ribbon for 200 rounds. For easy operation the tape should be laid in metal trunking, suspended on mounting on the underside of the receiver. In addition, created several new stores of large capacity. V. N. Paranin developed store MLO 75 cartridges that were a direct analogue drum magazine of the RPK. There was also a drum store 100 cartridges, created by Vladimir Kamzolova. The basis for this product were the solution, borrowed from an old project tank machine gun DT.
In the design of PU machine gun was widely used ideas borrowed from machine gun RPK-74, which was created in the early seventies. The updated version of “machine Gun with unified submission”, which was designated as PU-1, the impact of the machine gun has remained the same. Some sites have been borrowed with minimal changes.
Gun PU-1 store 100 cartridges.
When you create a project IP-1 in the design of basic weapons, some changes were made. Also changed some elements of the power belt. So, to improve the reliability of the weapon was made to completely recycle the tape. As before, the gun was to squeeze the cartridges from the tape, however, has seriously changed the design of the links. Form of link with slight modifications was borrowed from the ribbon of the NSV machine gun. As part of this revision slightly increased the distance between the cartridges, which ribbon becomes more flexible. To apply the new tape had to redesign the receiver and the upper receiver.
The development of the project IP-1 lasted until 1976. By this time Y. K. Alexandrov became the Deputy chief designer, which works on the theme of “Poplin” was headed by A. I. Nesterov. Most of the work on updating the gun designers of Izhmash held under the guidance loop.
In 1976, gun PU-1 has undergone several tests, including at the site of the Ministry of defence. The gun showed good characteristics, including high reliability. Complex modifications will get rid of weight problems, primarily delays when shooting. The weapon worked fine in the ribbon and in the application stores.
However, a potential customer in the person of the military Department showed no interest in the new weapon. By this time, was completed a competition to create weapons under patron malinowsky, the results of which have been accepted on arms AK-74 machine gun RPK-74. Gun PU-1 had a higher performance, however, was not adopted. Against this weapon there have been some arguments. In particular, the military decided that the operation of the gun with the uniform flow will be difficult. It was mentioned that the gunner, in the pouches which have the necessary ammunition in eight sectoral magazines (360 rounds), will not be able to carry additional boxes with ribbons. Thus, the main advantage of the project is not interested in the military.
The machine gun IP-2
In 1977 the project “Poplin” was further developed. It was decided to change priorities. The main way to power the guns of PU and PU-1 was considered the store. The tape was seen as a Supplement. New gun IP-2 has been proposed as the main power band. Accordingly it was planned to rework the layout of weapons.
The machine gun IP-2. Noticeable the new layout of the gas engine.
In the course of such modernization the gun was fitted with a receptor tape that is located in the upper part of the receiver, and the window store in its left wall. In addition, the gas tube of automation has shifted under the trunk. Also changed the method of ejection of the cartridge cases and the firing mechanism has lost function of a single lamp. It was fired from the rear sear (without pre-feeding of a cartridge in the chamber) with rate up to 700-750 rounds per minute. The receiver mechanism of the tape had the possibility of realignment: munitions could be used both side Windows.
The machine gun IP-2 on rate of fire was superior to all previous constructions of family and serial RPK-74. However, a number of design features, such as overly complicated receiver tape, affecting the reliability of the weapon. During testing, it was determined that the previous IP-1 is more effective, easier and more reliable new IP-2. The fate of another modification “of a machine Gun with a unified filing” was completed after the tests.
Final weapon, developed under the theme of “Poplin”, became an experienced hand gun PU-21. This sample was an improved version of the IP-2 corrected. The overall layout and principles of operation remain the same. All changes are in fact related to the operation of the receiver and automation, aiming at improving the reliability.
Gun PU-21 with a ribbon in a metal box.
The basis for the design of a machine gun PU-21 was the receiver, slightly resembling the previously used modified versions of the box RPK-74. In the front part of the receiver fastened to the barrel length 590 mm with the gas tube. The latter was located under the barrel. Because of such a configuration gas engine a mount for a bipod was mounted above the barrel. When folded, they had to lie down on the barrel top.
In the upper part of the receiver were placed receiver tape. His units were supposed to eject cartridges from tape nerazryvno and submit them on line disilane. According to the results of the project IP-2 it was decided to abandon the possibility of changing the feed direction of the tape. Thus, PU-21 received bullets through the window in the left side of the receiver. Under the window for receiving tape provided for the receiving window of the shop, is on the same level with the bolt. A machine gun with a gas automatics had a rotating bolt to lock the trunk. The spent casing extracted from the chamber and thrown down to the right. The trigger mechanism allowed only automatic fire gun, it was fired from an open bolt. On the bottom surface of the receiver were mount box with ammo belt.
The prototype machine gun PU-21 was fitted with a wooden accessories: foregrip, pistol grip and butt. The handguard was designed specifically for the new machine gun, while the handle and butt were borrowed from existing weapons. Slim neck butt allows to keep the weapon with his free hand.
Gun PU-21 had a total length of 1060 mm. Without ammunition, the weapon weighed 5,7 kg With tape 200 rounds of ammunition and a box for her, the weight of the gun was up to 8.5 lbs. For a machine gun bunker could use ribbon for 200 rounds, standard automata-based stores to 30 rounds or magazines from the RPK-74 with 45 cartridges.
According to reports, the experimental shop of Izhmash in 1978 gathered experienced gun PU-21, however, information about the testing of this weapon is missing. Weapon designers got a new job, which had to stop all work on the theme of “Poplin”. The sole is made of PU-21 went into storage.
The results of the project
Some sources mention that the authors of the draft PU-21, having completed his development, decided to patent the layout, but have not applied. They soon began working in other projects and never returned to the subject of weapons with so-called unified supply of ammunition.
Shortly after finishing work on “Poplin” Soviet gunsmiths learned of similar foreign developments. In the late seventies Belgian company FN introduced the Minimi machine gun, capable of use as a tape and stores. The FN Minimi machine gun and various weapons on its base still in use in many armies of the world. The Soviet project of PU and its modified versions were allowed to gather the necessary information, but has not led to the appearance of the production of weapons used in the armed forces. As a result the primary means of fire support office and a platoon in the national armed forces is still a manual machine gun RPK-74, use only shops with a capacity of 45 rounds.