I was playing in unmodded KNOX R/S, when I repawn with a 14 shot LAW, and a 41 shot steyr. Neither shot anything, and steyr's ammo didn't even decrease. Here's my recollection of how the weapons acted:
mp5: didn't fire, 41 shots
ak: fired, no bullets came out, 255 shots
barret: no bullets came out, 15 shots
Minigun: no bullets came out, 55 shots
socom: no bullets came out, 14 shots
LAW: no missiles came out, 14 shots
chainsaw: no damage, unbelievable screen shake, 55 shots
I was then banned for trying to show someone the bug via the LAW and AK. Note that I could not inflict damage on anyone.