As a favor to the rest of the gun-owning world, hang a sign around this guy's neck. (Ok, this might be unkind. I do not know him, but I had to vent my first reaction.)
Take the gun to a reliable Smith & Wesson certified gunsmith and have him check the gun out and present your friend with the bill. If he is a friend, he will at least pay half (recognizing that accepting a free job has put some responsibility on you).