Customer: On my AR, the bolt locks to rear on an empty mag when you fire the last shot, but it won’t lock to the rear when I manually operate the bolt catch. What’s the problem?
Me: You. You’re the problem. You’re either pushing the wrong part of the bolt catch, you’re not pushing it hard enough, or you’re releasing the bolt catch too soon.
Customer: Could it be the detent?
Me: No. It’s you. If it operates with an empty mag, it has to operate manually.
I told him that if he wanted to bring it in, I’d be happy to show him how to operate his bolt catch.
"I know guns, especially these M16s, and I'm telling you, somethings broke on this one. Every time I try to lock that bolt open the magazine falls out. It can't be me, it must be the gun. Dang BCM - I knew I shoulda bought a Colt."