Board Thread:General Discussion/@comment-111.68.32.71-20131007122233/@comment-209421-20140414033337

That's not the key issue, though. Small ballistics don't have the kinetic mass to continue moving at a high speed through a liquid. Pistols, rifles, even anti-material rounds have limited effectiveness through water, because the pressure displacement from the shot itself is the issue. What you COULD use is a fully mechanical setup for a harpoon launcher - a sealed spring chamber so that the kinetic energy isn't diluted through water, but I don't see how much more effective it would be to a gas-based weapon.

Seriously, underwater combat is restrictive in most forms - torpedos and harpoons are the primary underwater weapons for a reason.