Some here scoff at the idea of Birmingham using 10% more charge as a proof load. Certainly, this is not ideal; but with a quick look over Hodgdon and A-Square data, one finds a 10% charge increase can create a pressure increase of 20 to 50 percent, depending on the powder and cartridge. Proofs need 33 to 44 percent over pressure (SAAMI), so this is pretty good as far as rules of thumb go.

Similarly, using the data to compute K.E. rise compared to pressure rise indicates the German approach of requiring 25% more energy also seems to give suitable pressures, but on the high end of the proof range.