This is a pic of a 300 Win. Mag, which came to me for re- threading.
1, The information I got was that the original T8 can had attached itself in a permanent fashion by rusting itself on. The owner took it upon himself to remove it by clamping the can in the vice and using a wrench on the barrel and some heat on the can eventually removed it, damage so far, two ugly wrench marks on the barrel. "he should have stopped there"
2, He then decides probably correctly that the thread is too badly corroded and shoe shines it down to a finish which is too small in diameter to take a new 1/2x20 can. He decides 14x1 will do so he take the diameter of the barrel down to a fairly near working diameter using an angle grinder and files, gets a hold of a 14x1 die nut and "Threads" the barrel. "he should have stopped there," he has also got a variation for his new can.
3, He purchases his new can and believe it or not gets a reasonable fit on the threads. "he should have stopped there"
4, He takes rifle and ammunition to the target, fires 3 rounds and actually gets a group not too far off the mark, makes his correction, the first round is centre and a little bit high, "HE REALLY SHOULD NEVER HAVE STARTED THIS", The next shot sends the can some 60-80 yards into the loch behind the target, how do you explain this to your FEO when you ask for another variation for a replacement can.
This was what I was told by the guy in the shop who asked me to re-thread for the new can, I test fired the rifle and it shot extremely well.
I will leave this up to you to give your opinions on this.