I have a Swedish 96 action almost blown in half.
Bolt remained locked and in position, ~ 1 sq in of right sidewall of receiver has been blown completely off, Right rail fractured right in front of rear bridge. Stock was broken in 2.
No overpressure load.. Factory..
Case failed at primer pocket.. (probably a seam in case blank)
Expanding gas has nowhere to go.. The thin wall of early Mauser actions where locking lugs must rotate, is the weak point. A couple gas relief holes (like on modern bolt rifles) Might have saved action...
Since an overpressure action failure, is not involved in ALL rifle failures. Why bother testing for action strength when the cartridge brass, as posted above, is almost always the point of failure in a rifle?? Main things to worry about are, gas/debris going to rear, and gas handling at front of action. Testing how an action handles that might be worthwhile.. Testing action failure mode with an overload of improper powder is a waste of time...
The military has experimented with, and deployed enemy caliber ammunition designed to blow up a rifle... High explosives instead of powder seem to provide a sure fire action test to failure load.. This looks pretty likely... AK-47 blows up in the hands of a terrorist - YouTube
Bad brass, Excessive (extremely) headspace. Extremely loose chamber, all cause problems
There is not an action out there, that provides ANY support for the extractor groove on a rimless cartridge.
Case base (yes fairly thick usually) has an extractor groove that is supported only by air.. Rimless cartridges of course..
Loading test rounds that exceed the strength of the weakest part, (the brass) is only going to cause the problems Speerchucker has already brought up..