The adoption of the AK-47, despite a number of shortcomings, was undoubtedly a great achievement of domestic weapons science. The machine fell in love among the troops for the simplicity of the device, reliability and compactness (in comparison with the SKS carbine). However, it turned out to be not cheap and the rearmament laid an exorbitant burden on the war-drained economy of the country and threatened to stretch out for decades. The production of new assault rifles only slightly exceeded their decline as a result of intensive combat training. Therefore, SKS carbines were in service even with motorized rifle units until the mid-60s, and even more in some branches of the armed forces. In addition, the increased requirements for the mobility of troops forced to revise the weight load of the equipment of each soldier, the mass of weapons with ammunition in the composition of which was (for the AK-47 with four magazines and 120 rounds, a belt, a bayonet, a pouch and a spare part) 9 kg. All these requirements will acquire legal force only in 1953, when the tactical and technical requirements for a new lightweight machine gun were worked out. For now, let's go back to 1951.
The shortcomings of the AK-47, which were not eliminated either before it was put into service or during the establishment of mass production, prompted a number of other gunsmith designers to continue work on the design of machine guns of their designs, and the GAU took a passively wait-and-see position (what if it works out), and The DOD funded them. The pioneer of these works was the representative of TsKB-14, the talented Tula designer G. A. Korobov. Already in 1951, he presented for field tests his automatic machine of a very original design with a rarely used automation scheme - a semi-free shutter. In general, the machine was distinguished by its simplicity of design and manufacturability of parts (and, therefore, low labor intensity and cost), most of which were manufactured by cold stamping from sheet steel. The absence of a rigid locking unit not only eliminated the time-consuming operations for its debugging, but also unloaded the receiver, which made it possible to significantly reduce the mass of the machine (by 0.65 kg). An important economic factor was the use of a serially produced AK-47 magazine without any additional modifications. The principle of operation of the automation was based on:
- on unloading the chamber with grooves of a large cross-section, which ensured early and effective unloading of the chamber;
- on the support of the sleeve in the chamber during the shot with the free mass of the inertial body acting on the sleeve not directly, but through the lever, which created the necessary support of the sleeve with the small mass of the free inertial body.
Before firing, parts of the bolt are in the extreme forward position, namely:
- a combat larva with a drummer and an ejector rests on the trunk stump;
- the lever is in an almost vertical position, resting with its lower edge on the stop of the receiver jumper in its middle part, with its neck on the combat larva, and with its upper feathers perceives the longitudinal pressure forward from the bolt stem, supported by a return spring.
When fired, the pressure from the sleeve is transmitted through the combat larva to the lever, which, resting on the box stop, turns and throws the bolt stem back. During the turn of the lever, the pressure in the barrel drops to atmospheric, and the bolt stem receives a supply of kinetic energy sufficient to roll back to the extreme rear position. However, it was not possible to fully evaluate the Korobov assault rifle in all its characteristics due to the low survivability of the barrel coupling. The fact is that the main part of the chamber, with the exception of its rear, was formed in the barrel. The barrel was fitted with an interference fit in a sleeve that formed the bottom walls of the grooves and the rear of the chamber 8 mm long.
In 1952, modified machines were presented for testing on the basis of the conclusion of the USV GAU dated 08.24.51.
Tests carried out in 1952 showed that in terms of the reliability of the operation of automation in normal and various operating conditions, in terms of the survivability of parts, the Korobov assault rifle satisfies TTT No. 3131-45 g. simplicity of design, development and manufacture. At the same time, the tests revealed low service strength of many parts and a number of design flaws in individual units, the list of which took two sheets.
In 1953, TsKB-14 submitted modified Korobov assault rifles for testing. For these machines, the grooved chamber, with the exception of the bullet entrance, was formed in the barrel sleeve, almost all parts were strengthened, and the cadmium plating of moving parts (a rather expensive and harmful production) was replaced by phosphating.
By this time, the tactical and technical requirements for the new machine gun TTT No. 006256-53 were developed and tests were carried out for their compliance.
The test results showed the feasibility of most of the modifications to the machines. However, there was
a number of features inherent in the applied automation scheme have been identified:
- the initial velocity of bullets is on average 38, 5 m / s lower than that of the AK-47 due to the presence of grooves in the chamber;
- uneven rate of fire both in normal and in deteriorated operating conditions, the change in which reached 185 rds / min. (three times more than AK). The reason is the specific work of the self-timer (constructive), which acts as a counter-rebound of the shutter stem and the slower of the rate of fire;
- shooting in bursts with regular blank cartridges is impossible. Development of a reinforced blank cartridge is required;
- the muzzle flame when firing is much greater in magnitude and intensity than that of the AK (force length 200-250 mm versus 30-40 mm), which is explained by the lesser completeness of the explosive decomposition of gunpowder due to the use of a semi-free breechblock. The pressure curve in the chamber has a lower maximum pressure, a longer time of pressure rise to maximum, a longer time of pressure action until the bullet leaves.
Despite the obvious shortcomings of the system, the two positive points noted - the mass is 465 g less than the AK-47 and the costs in machine-hours are about 2, 2 times less than for the AK-47 - undoubtedly influenced the final conclusion: about the need to continue further work on the Korobov assault rifle, it is advisable to make a small series (about 20 pieces) of such assault rifles and subject them to extensive comparative tests with Kalashnikov assault rifles at the Shot courses at the rifle tactical committee, at the test range and long-term operation in the army. Which was done.
On the study of the automation of the Korobov assault rifle, research work was carried out, which substantiated the almost impossibility of creating a fail-safe sample according to this scheme. But G. A. Korobov never gave in to technical difficulties and continued to work out the system until 1956.
But it will still be ahead. And in 1953 it seemed that the "star" of MT Kalashnikov and his AK was already fading.