Originally Posted by Hunter Customs
Now as for stopping power or knock down power even if they don't exist, there is a thing called power factor, which is what I go by
Power factor of a 115 gr 9mm FMJ bullet moving 1180fps is 135.7, power factor of a 230 gr 45 FMJ bullet moving 850 fps is 195.5, I'll take the 195.5 any day.
"Power factor" is just applying a simplistic equation to something that's not so simple in real life. As 45_auto showed with his Suburban example, your "power factor" doesn't really mean all that much when actually applied to real-life examples.
When I was a kid I was obsessed with the many different attempts to measure the "power factor" difference between 9mm and .45 ACP. At first I followed Elmer Keith's equation, then I switched to Chuck Taylor's simpler one. And by now I've learned that the experts have basically given up trying to measure the difference: With good modern hollow points the difference is barely discernible, if at all.