Underwater, ordinary-shaped bullets are inaccurate and have a very short-range. The APS fires a 120 mm (4.75 in) long 5.66 mm calibre steel bolt (specially designed for this rifle and has been mistaken as 5.56 mm). Its magazine holds 26 cartridges. The APS’s barrel is not rifled; the fired projectile is kept in line by hydrodynamic effects; as a result, the APS is somewhat inaccurate when fired out of water.
The APS has a longer range and more penetrating power than spearguns. This is useful in such situations as shooting an opposing diver through a reinforced dry suit, or a protective helmet (whether air-holding or not), thick tough parts of breathing sets and their harnesses, and plastic casings and transparent covers of some small underwater vehicles.
The APS is more powerful than a pistol, but is bulkier and takes longer to aim, particularly swinging its long barrel and big flat magazine sideways through water.