Conventional firearms do not function well when fired underwater nore are they affective at all. A typical projectile fired in such a manor will not travel, lethally, more than 6 feet or so unless special cavitating ammunition is used.
Typically only exists for larger cannon rounds.
Confused, what is the issue you're reporting?
The only guns that even fire underwater is the special rifle for that purpose.
They aren't intended to function under the water only the special purpose MX rifle does.
Make sure to read up on the game/it's indended features in the future.
How about a combat knife? Many normal weapons WILL function underwater, it just isnt realistic to portray them as being nearly the killing machine as their above water counterparts.
They aren't being portrayed that way at all. With the given rifle in the SP mission you have to be within about 10m of someone for it to even have a chance and even then it takes quite a few rounds to take someone down. There's a history of specially built underwater rifles. Sure they're super rare I agree but they are there in the real world.
My experience is gun powder dosen't work well under water. But if you have something to the contrare i'd love to see it.
It's also common knowledge that if you don't clear water from most rifles after coming out of the water it will blow up in your face.
modern weapons use "cartridges" made of brass (typically) casings which contain the propellent (not always gun powder) primer, and round. This new fangled contraption is waterproof to a certain depth.
http://www.youtube.com/watch?v=WOoUVeyaY_8
The above weapon did not malfunction when water was applied
Weapons can be made tough enough to withstand these preasures but it is a good rule of thumb not to fire a weapon when submerged (water in barrel from rain in such should not explode).