Re: Serious trouble with AR-15
Installed a bunch of these triggers, they are my favorite and the price versus performance is good.
Out of the dozen or so I have installed, NONE required any metal removal. I suspect your smith didn't read the simple directions that came with it, and tried to "fix" it. If the trigger didn't work right, JP would make it right, they have a even replaced a trigger for me, when a heavy handed buddy kept pulling the trigger, with the safety on, until he broke it.
Filing on an AR trigger, usually results in doubles, and it's dangerous, the rifle can ( but normally won't)fire out of battery ie the bolt not fully locked. Don't try to keep shooting it, get it fixed.
Me, I'd get the trigger replaced, at the smith's expense. His dremel/file work as removed the hardening on the sear/disconnector/trigger, and it won't hold adjustment in the future, that's why those parts are hardened. And why files are poor practice there....