Interesting.
My take is that whatever tightly fitted system you might select, it will wear with the opening and closing action more than it ever will with firing stresses.
Build interference and wedge fit all you want, it's going to wear and 'shoot' loose although the actual 'shoot' part isn't causing it.
I'd bet that with any sound lockup system if you could close the thing once and somehow pressurize the vessel 100K times to simulate firing and associated stresses, you would measure no wear upon disassembly.
These things don't stretch apart, they grind themselves apart.
