to bent internal parts they tried to force into place. Front sights battered from guys trying to take them off. One gun had to have about $75 to $80 parts replaced where he had destroyed them trying to force them into place. Just about any part that can be put into an AR has been put in wrong and the guy has to pay a lot extra to replace the parts. We get at least 1 gun a week that the owner gave up on and wants us to fit all the parts or that the owner says he knows how to do it but doesn't have the time. That is the excuse most used.
I know several of the guys on here have built their own AR and that is fine but if someone asks me if I recommend them building their own AR I will do my best to talk him out of it. The AR is one of my favorite rifles and I hate to see one all boogered up inside by someone that has no idea what he is doing. Why bet your life on a gun that might work.