Caliber: 5.6×39 mm MPS
Action: Gas operated, rotating bolt
Overall length: 823 mm (butt retracted), 615 mm (butt collapsed)
Barrel length: n/a
Weight: 2.4 kg less magazine; 3.4 loaded
Rate of fire: 600 rounds per minute (in air)
Magazine capacity: 26 rounds
The APS (Avtomat Podvodnyj Spetsialnyj = Special Underwater Assault rifle) was developed during the early 1970s at TSNIITOCHMASH (Central Institute for Precision Machine building) by the team lead by V. Simonov. APS underwater assault rifle has been in active service with combat divers of the Soviet and Russian Navy since circa 1975.
The APS underwater rifle is designed for special underwater cartridges, which fire 5.66 mm needle-like projectiles 120 mm long. Projectiles are drag-stabilized using a hydrodynamic cavity, generated by the flat point of the conical nose. The cartridges uses standard 5.45 x 39 cases, sealed from water. The APS itself is a relatively crude, smooth bore arm, with a gas operated, rotating bolt action. It fires from an open bolt. Single safety / selector switch is located at the left side of the receiver and allows for single shots and full automatic fire. The gas system features a patented self-adjusting gas valve, which allows the gun to be fired both underwater and above the water, in the air. The rate of fire under water, as well as the effective range, depends on the actual depth. Sights are crude: a non-adjustable open notch rear and post front. The retractable buttstock is made from steel wire. The most complicated thing in the whole design is the feed system, which includes several parts to avoid double and even triple feed with the extremely long projectiles. Unusually deep (front to back) magazines are made from polymer and hold 26 rounds.
It must be noted that while APS could be fired “above the water”, it should be done only in the case of emergency. According to the available sources, the expected service life of the APS when fired “in the air” degrades severely, and the effective range is limited only to several tens of meters. So, the APS is useful only under the water, where it is quite effective.