Slostin machine gun

The Slostin machine guns are a series of gas-operated, self-powered Gatling type (multi-barreled) machine gun prototypes, developed by Soviet designer Ivan Ilyich Slostin beginning in the late 1930s and up to 1949. Of the three known prototypes, the first two were the chambered for the Soviet 7.62 round, and the last one for the 14.5 mm.

7.62 mm prototypes
Slostin's first prototype (chambered for the 7.62×54mmR) was field tested in 1939, but it proved unreliable. Although it briefly archived a rate of fire of 3,300 rounds per minute, the gun seized after only 250 rounds, due to deformation of its parts caused by heat buildup. The model field tested in 1946 was somewhat different; although its reliability was much improved so that it could now fire about 1,500 rounds in a sustained burst before overheating became a concern, it no longer reached the 3,000 rpm rate of fire claimed by its designer's, but fired at a more sedate 1,760-2,100 rpm. The dispersion exhibited by the bullets shot by this 1946 prototype of Slostin was 6-7 times greater than that of the SG-43 Goryunov machine gun.

The 1946 model has a stationary breech and eight movable barrels. Its barrels move not only in the circular, typical Gatling fashion, but also move back and forth longitudinally, parallel to the axis of the bullets. Each barrel has its own gas cylinder, which houses a piston that is rigidly connected to the barrel adjacent to its right (from the shooter's perspective). The barrels are fired sequentially by a classic firing pin released from a sear. Upon firing one barrel, the expanding gasses act on the piston of the barrel next to it (and which is the one that had just fired previously) eventually pushing it forward to the fullest extent possible so that it can start loading a new cartridge. The feeding cycle of a barrel then lasts an entire revolution of the barrel block, with each barrel gradually being pulled back until it seals the cartridge and is ready to fire again. This motion is driven by a bearing affixed close to the rear end of each barrel, and which rides on a helical groove in the receiver during the feeding cycle. The 1946 Slostin machine gun was fed by a non-disintegrating metallic belt. For the infantry field tests, the 7.62 mm Slostin was mounted on the Sokolov carriage of the PM M1910 machine gun; photographic records show that it was also put on a pylon-type anti-aircraft mount with a large drum housing the ammunition belt.

14.5mm variant
Slostin built a 14.5×114mm prototype which was tested in May 1949, but this differed rather substantially in design compared to its 7.62mm predecessors. The main difference was that the barrels no longer moved back and forth (parallel to the axis of rotation or relative to each other), but they were rigidly bound together like in a traditional Gatling. The gas pistons now acted directly on the bearings which followed a helical groove in the receiver. Still, the 14.5 mm variant had problems with striking primers off-center due the difficulty in decelerating the now massive block of barrels, and the problem was considered unsolvable without radically changing the design so this variant was abandoned as well.