Game starts up runs fine for me. I get crashes/lock up requireing reboot like this only in vehicles. They seem to happen due too lag? Its only when I stop and start moving again quickly.

http://en.wikipedia.org/wiki/ASM-DT_amphibious_rifle

This is as close as you can get that I know of, it still fires spears/bolts underwater but does have a rifled barrel and can fire regular rounds when out of water.

Underwater, ordinary-shaped bullets are inaccurate and very short-range. The APS fires a steel bolt caliber 5.66 mm (specially designed for this rifle and is often mistaken as 5.56 mm) and 120 mm (4.75 in) long. Its magazine holds 26 cartridges. The APS's barrel is not rifled; the fired projectile is kept in line by hydrodynamic effects. As a result, the APS is somewhat inaccurate when fired out of water.

It`s a spear gun, the barrel is not rifled it`s NOT A RIFLE. It shoots a very short spear/bolt.

You can`t fire pistols/rifles etc under water in RL, they can explode and kill you if you try. (You need a spear gun, I`d vote for a spear gun). Also shooting at fish from above into the water does not work well. Bullets tumble and loose speed very quickly, or in case of some types (hollow points) explode on hitting water, as well as light refraction issues. vote down, who care to shoot fish anyways?.