On YouTube are videos of a man shooting cast iron and steel skillets using various handgun cartridges. Good insight. The 9mm's just blew through. 22's made little dents as did others like 38's. The 45 ACP never penetrated any of the skillets, leaving only dents. Results were in line with US military tests after the war. Shooting a GI and German helmets with 45's and 9mm's, the 45's just made a large dent, 9mm's penetrated completely one side and either dented or passed though the opposite side. Higher velocities and smaller frontal area were the key. Dangerous game cartridge from the dark continent proved like results. The mighty and massive 577 and 600 Nitro cartridges were not highly thought of as their penetration was far less the smaller, faster 500 Nitro.