Primer flow is an example of gross over-pressure. There really aren't any sure fire methods of determining the high end of safe pressure because most handguns operate at pressures well within the capabilities of brass casings. Also autoloaders often headspace by hanging on the extractor, so a flattened primer might not be telling you much.
My M&P has the best casehead support I've seen. I could run pressures high enough to loosen SP primers before the case would bulge. So I try to stick to published data.
Last edited by dla; 06/25/22.
