I am a firearms instructor at work and had to take a instructor development course.
I was gonna run the AR, but decided I'd use the ACR instead. First day I put 1500 rounds through it and had zero failures. Second day the same, 1500 rounds zero failures. Third day 1000 rounds and had one failure to fire.
I did not clean or lube the rifle through the whole course.
Total round count so far is about 10k. Only minor repairs and maintenance has been performed. I replaced the firing pin at about 8k. It's been almost flawless since the first round.