After 1800 rounds:
[ link to LARGER image ]
[ link to LARGER image ]
[ link to LARGER image ]
This should show that a decent AR15 even with a SS barrel can run reliably for thousands of rounds without cleaning.
During the man-down drills, I did "roll out" to start shooting once and noticd my Aimpoint was off (IE, it had been bumped or something - I never turned it off the whole class). Instead of messing with it, I stayed "in the fight" using the Aimpoint as a gross rear ring until I deployed the BUIS.