Sounds used from other games
 

I've noticed that the sound for the Mp40 and Thompson were also used in Medal of Honor: Allied Assault.

The M1 Carbine sound I've heard used by a Colt 1911 in the game Mafia.

Just a bit of trivial. :)

Well, It could be that they acquired the lisence for these weapon sounds from the same company that specializes in sound effects and such. I think some game developers do that. Not sure whether they did so for this game though.