What's the length of a turn/action?
If it's longer than a minute, there's no need to model it. If your turn/action is more like shoot turn 1, spend turn 2 reloading, shoot turn 3, then you *might* want to put something in, but I can reload an M16 in about 5 seconds, if I'm not counting rounds *and* while prone. Standing, I can reload a pistol in less than 2 seconds, and professional competition shooters have the reload down to under a half-second (I've seen photos of a guy firing the first shot off a new magazine before the falling magazine is below his belt!).
Reload rate is not an issue for modern weapons. Even Infinity, which has individual actions lasting about 10 seconds, does not include anything about weapon reliability or reload time.
Bayonet's idea isn't bad, but modern weapons just don't foul up that often. I've put rounds # 2-201 through a brand-new pistol (it had only had one proofing shot fired through it before I bought it), and have had not problems with it yet.
*IF* you wanted to include jamming, I'd suggest something like the Cyberpunk FNFF reliability rolls: IF you roll a '1' to-hit, then roll another d10 and subtract that roll from your total. If the number is negative, then you have jammed and need to spend a turn clearing the jam (slap, pull, rack the bolt/slide).
