No the underwater one had a funky magazine and much much longer rounds. This one's from that point in time where everybody thought tiny.
the cartridge shown is NOT for AO - 27 ; it's later experimental FSDS ammo for sniper rifles and MGs ammo for AO - 27, IIRC, had.
AO - 27 was a Soviet assault rifle, chambered for the 7.62 mm fin-stabilized flechette sabot round. The flechette itself had a body diameter of 3 mm. The overall.
AO-27 rifle - buses from