On the subject of barrels reacting to extreme pressure, here are a few exampls

Firstly - I read an article in Rifle magazine a few years ago where some one had inadvertantly fired a 7mm mag round in a 270 Weatherby mag rifle. The result was that the bullet jammed in the throat but the lead core blew out, leaving the jacket stuck in the throat. The action was of course found in various parts of the Mongolian desert & even proably little old New Zealand! The shooter still picks bits of metal & wood from his face when he shaves.

The second one is a Brno 25'06 rifle that I saw with a famous gunsmith here in NZ. Some one brought it to him, saying "My mate fired a 308 round in it". Strangely the 308 bullet went right through the barrel & there was no evidence of any harm done to the barrel. The action & bolt had taken the huge pressure and cracked into small pieces but still held together. the stock was in the same state but falling apart. I saw this rifle in this condition. This shooter has no issues while shaving (but probably decided to grow a beard)!!