Could you explain what you mean by "bullet setback against the feedramp"?
Sure. The bullet impacts the feed ramp just under the chamber after the round is stripped from the magazine. This can and does sometimes drive the bullet further into the case. This causes less space for the powder charge. This in turn causes higher pressure.
That 5.0 charge of W-231 could cause enough pressure to blow a case if the bullet was sitting right on top of it.
I'm not familiar with the PT92, does it have an unsupported chamber that allows that kind of blow-out?
Check your loads after seating and crimping them by trying to push the bullet further into the case. Do it by sitting the bullet against your bench, then pushing on the back/head of the case. You should NOT
be able to move it.