The Russian SPP-1 4.5mm underwater pistol can accommodate either a twin or quad-barrel arrangement with a cartridge in each which is inserted into the pistol's breech. The Chinese QSS-05 5.8mm adoption (or 山寨) has a tri-barrel pistol arrangement.
The Chinese also "山寨-ed" the Russian APS Underwater Assault Rifle to fire the Chinese 5.8mm rifle round.
* Thanks genkideskan, =GT, and chenium for the photos.
Russian SPP-1 (twin-barrel) vs QSS-05 (tri-barrel)
The Chinese 5.8mm underwater ammo
Chinese Underwater Assault Rifle
APS Underwater Assault Rifle
Other PLAN underwater toys.