The Shiryaev B-VI-307 (Б-VI-307) is a prototype Soviet underwater firearm.
The B-VI-307 was developed in the mid 1960s by D.I. Shiryaev of TsNIITochMash, with twelve copies being delivered to the Soviet army in 1969 for testing. The weapon was a testbed weapon used by the Red Navy. While the weapon's design was favorable, the darts were not liked by the Red Navy and rejected. The B-VI-307 was later tinkered with and developed into the more well-known SPP-1 underwater pistol.
The B-VI-307 operates very similarly to the later SPP-1; striker-fired with a striker that aligns with one of four cartridges in the barrels. The weapon is a smoothbore weapon, similar to the later SPP-1, which makes it somewhat inaccurate above water.
The B-VI-307 uses an interesting 4.5mm dart.