I actually have an article coming out soon on personal defense network discussing this. The term stopping power refers back to the late 1800's and early 1900's when smokeless powder came around. The more powerful powder lead to having to use jacketed bullets and lead to a decrease in effectiveness. The military wanted a larger caliber to stop rounds from simply going through a target and thus the .45 ACP was born.
Over 100 years later we have great advances in technology and using a larger caliber round to gain effectiveness is no longer needed. Carrying a
9mm with quality defensive ammunition is much more effective than a larger round.
BTW the difference in power from 9mm FMJ to 45 FMJ in blazer brass is less than 10%. Many people stay with FMJ in .45 ACP because the carry 1911 style pistols which have failure to feed issues because of the 2 piece feed ramp. They refuse to switch guns and believe in mythical powers of the .45 ACP that are actually severely outperformed by 9mm quality defensive ammunition (and even much less powerful rounds for that matter)
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