There is no way that a bad threading job would contribute to a chamber being permantly distorted. The kind of actual pressure that it would take to do that would have left the entire Rifle a pile of junk.
As Jerry said, in order for a material to be permantly distorted, you have to go beyond the yeild strength of that material. Most of the other components involved, mainly the brass case, will fail way before that point is even approached.
It's just a sloppy machine job. Sort of shows how bad things can be and a Rifle still actually function under normal conditions..........jackie
I can't say how barrels made from the best modern steels would act, but I have run across several older rifles that gave the appearance at least of the chamber and shank having swollen to the point that the OD of the threads was form fitted to the Receiver Ring, replacement barrel shanks being noticably looser than the shank of the removed barrel.
A couple of those were rifles I suspect were used for launching rifle grenades, and one which I didn't rebarrel , had a built on grenade launcher, that barrel being noticably swollen at the points where the gas port fixture and rear sight base encircled the barrel.
Could be that the cases used for GL blanks are much sturdier than standard cases, and wouldn't blow out at pressures high enough to deform the shank.
Hard to tell about military chambers, since most are a bit on the loose side to begin with, and barrels are often subjected to much higher heat when fired continuously for several hundred rounds during a battle.
Some Bolt Action military rifles develop internal bulging due to bad bores or defective ammo and resulting extreme pressures..
I've seen a few where the chamber became "jugged", swollen more at the front than at the rear, the difference being mainly that the rear was enclosed and supported by the receiver ring so it didn't get the chance to swell as much.
