Absent other information, one would have to assume SAAMI maximum pressure for all factory loads.

This would be 11,500 psi for 12ga.

They undoubtedly don't run that high but since they aren't loaded to a pressure but rather to a velocity within limits, assume they vary with lot number.

They work well with gas autos, and that's intentional.

My GUESS would be they average 10K to 10.5K.

"The price of good shotgunnery is constant practice" - Fred Kimble