halo reach has too many limiters on all the guns. Haven't tested all weapons thorough enough to say for sure. but theres what i got:
555 timer mod
plus or minus 0.25Hz
plasma rifle - best at 7.8Hz, maxed out at 8.4Hz
plasma pistol - best at 5Hz, maxed out at 9Hz
all turrets - it works i just can't see any change in performance
vehicle horn - it doesn't work over 6Hz