Heat can do amazing things, both good and bad, being bad as in the barrel Don mentioned.
On the other hand, although nothing to do about gun barrels, one big fishing boat I worked on long ago had the topping cable for the boom break. The end of the boom had a less than gently landing on the fishing net, and the 24" diameter boom bent down like a bannana about 2 feet. No kink, just a smooth bend about 8 feet long. We put into Samoa for repairs, and a little Korean guy showed up the the most gigantic Oxy/Acy rosebud I'd ever seen, the head part about 8" in diameter. After setting up, he proceded to heat the top of the boom at the bent section, then cool it with a hose, and after about two days, the boom was again as straight as an arrow. After welding on a huge strongback, we set back out to sea and never had a bit of problem with the boom repair.
As for the barrel discussed here I agree with making it into pistol barrels, count it a lessen learned and move on.
John