Yeah, I knew about the Nagant, but their scarcity - plus Hollywood’s and most of the publics’ ignorance, allowed them to use standard revolvers and then dub in the Pfftf sound.
Motion capture, with a 3D headset. Tied to a robot, with a multiplexed signal system, on the bottom, next to the Titanic, or in a live volcano. No risk of life, no real bottom time limit, imagine the dexterity.