I'm not sure how it would be done, however the case would have to be exactly identical in capacity to a standard case to ensure an accurate test. Some possibilities would be a pressure sensitive paint on the inside of the case that was calibrated at the right pressure. Maybe also a small closed vessel in the head of the case (exposed to the powder of course) that would rupture at the max pressure. I'm going to think on this a bit more, any thoughts? Would you be interested in something like this?