When I had a gun smithing shop, I had a guy come in asking for a muzzle brake for his "fire breathing" 7mm Mag. I told him $165 installed. He said that he found brakes much cheaper, and would do it himself.
About 3 weeks later, he came back in with the same rifle and the threads(don't know who threaded it for him)ripped off of his barrel. He now wanted a new barrel and a brake. After 30 minutes of conversation, he said that his brother(a machinist)threaded the barrel. Then he ordered a Schrewd Precision brake, and threaded it on his rifle. Upon firing the first shot, the brake was gone! He forgot(or didn't know), that he needed to drill and ream his brake out to .020 over 7mm! Dude was lucky he didn't kill, or injure someone!
