I can top all of these stories. I bought an unfired custom 300 RUM off gunbroker that had a Shilen heavy barrel with a muzzle brake. I started doing some shooting to try and get it on paper. I usually bore sight at 100 yards as I am usually close at that distance. Couldn't get it on a large piece of cardboard. Tried 50 yds, still no dice. Finally shot at 25 yards and had a nice side profile bullet hole in the cardboard. Shot a couple more with the same result.
Took the rifle over to a buddy's house and we figured out the problem. Chambered for 300 RUM, 30 cal orifice in the muzzle brake, bore diameter .338! After about a month, much wailing and gnashing of teeth and lots of stress I was put in contact with the gunsmith who replaced the barrel with the proper one at no cost. He said that the fellow who had done the original work no longer worked there and he was doing it all himself.
It shot in the .3's when it came back and I sold it to a happy buyer. Just didn't want it any more after all the stress. I'm fortunate that the bullets didn't blow the brake apart after rattling down the oversize bore.
Another time I bought an MRC action here on the fire from its second or third owner, action had never been barreled. Sent it off to my smith to be barreled, who subsequently discovered that someone had started to true up the action threads to oversize but had stopped part way through.
The seller, who was as befuddled as me, offered a refund but he had sold the action due to medical bills and I didn't want to do that to him. I had it trued up the rest of the way and the barrel installed. It turned out pretty nice but I sold it as well.
I seem to have the reverse Midas touch when it comes to second hand firearm purchases.
