One thing I can say is that I'm always a bit wary of the "soft brass" theory. I'm not saying that it should ever be ruled out, just that I'm wary of it.
Many years ago I had pretty serious high pressure dramas in an old rifle shooting factory ammo.
Several gunsmiths said without a doubt the factory brass was "soft", and they were sure that was the problem.
I'm not talking about leaky or loose primer pockets here. This was a situation where the entire case head had expanded into the bolt face, locking the action up, and primer pockets looked they had opened up to twice the normal size.
On advice from the smiths who had examined both the rifle and the cases, I went out and bought a different brand of factory ammo. The smiths were certain that there was no problem with the firearm and that the problem was definately caused by the ammo I had first used having soft brass. "A bad batch" they said.
Well I tried out the new different brand of ammo, and guess what, it promptly did the same thing. Yup, exactly the same, with massive head expansion locking up the action, and massive expansion of the primer pocket.
That's the reason behind my being a bit wary of the old "soft brass" syndrome.