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Tests shown excellent flatness and penetration of the flechette sabot rounds, but also, a slightly lower accuracy, comparing with common rounds.
The AO-27 assault rifle, designed by D.I. Shiryaev in 1961, was a part of an experimental complex weapon - flechette sabot round, that had been under development in NII-61 (later - TSNIITOCHMASH) since 1960. By this time, was completed a number of studies, aimed at improving the efficiency of firing AK from unstable positions (standing, from the knee). As a result, it was decided, that the most acceptable solution of the problem is lowering the recoil momentum. To save, and even to increase the range of a direct shot, the caliber needed to be lowered.
By a similar conclusion earlier arrived in the U.S., where was developed a 5.56 mm round and an assault rifle for it. Developing of a domestic counterpart of the cartridge has been initiated by the head of the "Cartridge department" of NII-61 V.M. Sabelnikov. As an alternative, the "Aviation weaponry department" of NII-61 suggested to check the possibility of using the flechette sabot round for the same purpose. A hope for success gave the fact, that by this time the flechette sabot shell for the 100 mm anti-tank gun T-12 "Rapira", had been already made. The design of the cartridge with a feathered arrow-piercing bullet, and a detachable leading two-sector tray for the assault rifle-type weapon was developed in 1960 and protected by the copyright certificate N 22527 with a priority from the 1 of June 1960.
The authors of this invention are V.P. Gryazev, P.A. Fadeev, A.G. Shipunov and D.I. Shiryaev. The round was given an index OPS (Operennyj Podkalibernyj Strelkovyj, what is translated to Feathered Sabot Rifle). The AO-27 assault rifle for this round, was developed in the 1961 beginning. OPS round and AO-27 assault rifle represent worlds first shooting complex of this type. Later, americans tried to implement this idea, but their long-standing efforts in this direction were unsuccessful.
AO-27 has a vapor-automatic with removal of powder gases through the side hole in the wall of the barrel. As a barrel were used regular barrel blanks of 7.62 mm, which had a regular rifling profile, but rifling is flatter. The rotation of the bullet contributed to a clear separation of the sectors of pallets, leading a bullet down the barrel. In addition, by rotating aerodynamically stabilized bullet went averaging of eccentricity of forces acting on it, and therefore reducing the spread of hits. Bolt - rotating, with two locking lugs.
Stem bolt is made constructively together with a rod, ending in a gas piston. The return spring placed in a hollow rod of the gas piston. AO-27 has a striker type firing mechanism with a long course (almost equal to the course of the bolt) drummer. This was made to increase the cycle time of the automation, to reduce the rate of fire. The trigger is the simplest type one, consisting of a trigger, rotating sear, self-timer, and the disconnector. Trigger mechanism provides automatic and semi-automatic fiing. The fire/safety mode selector is located on the trigger guard, behind the trigger, similar to the self-loading rifles SVT, and has three positions: safe, semi-auto and auto. Sight consists of a rear sight and front sight.
The first variant had a dioptric rear sight and front sight was on a gas chamber. In developing the complex, on the recommendation of military commandment, rear sight has been replaced by the usual sectoral adjustable sight, and adjustable front sight moved to the muzzle of the barrel.
Shooting is performed with the so-called front-sear, ie with moving parts in the forward position. According to reports of the chief designer during the complex tests AO-27 advantages compared to the AK were overwhelming. In particular, the range of a direct shot was 530 m, against the 356 m for AK.
Recoil momentums were 0.5 kg/cm for AO-27, 0.78 kg/cm for AK. When shooting at a distance of 1000 m altitude trajectories were respectively 3 and 10.5 meters. The large initial velocity of the bullet of the OPS round (1060 m/s) and the lateral load given the AO-27 a significant advantage in breaking through barriers such as the trench parapet. Firing short bursts from a standing position shown, that the dispersion of bullets of AO-27 was much smaller as compared to the AK. But due to the weak stopping power and high cost of the round issue has been left in the category of research.