10 mm

[Flashover16]

I still question whether those loads that tore up the gun were over pressure. Anyone loading could make an error. Unfortunately, there is no way to ever know. You can't weigh the powder charge after shooting. The true cause is speculation unless u intentionally overcharged one.

well this is all speculation but!
Generally speaking all this my gun blew up and it was a hot load, usually boils down to a squib> then things get really nasty as there really is no where for the pressure to go except outward to the path of least resistance.
course over loads do occur but if you are suing a bulky powder the chance is highly reduced.