A few years back I had an upper receiver for a Colt AR 15 customized. New heavy target/varmit barrel, free floated handgards, basically everything you could do and keep configuration close to original. The gunsmith, one of the better AR 15 gunsmiths and a nationally ranked HP shooter did the work, and sent the completed project to me before wanting payment. He wanted to make sure it was ok. I have learned since that he requires payment before delivery so he must have been burned or had a few problems.
