There are only a couple of games I can think of that have weapons that sound even remotely realistic. Probably the closest thing to genuine firearm sounds in a game was Battlefield: Bad Company, but even it failed to capture the raw sonic power of actual guns. I don't get why audio directors, including the ones for Halo, saw fit to make field recordings of weapon sounds only to process the shit out of them. Having been to the range more than a few times myself, nothing beats the loud, sharp pop of an actual firearm.