IMO energy is a big factor but you need to use common sense also. A FMJ 308 has a ton of ME but it doesn't transfer much of the energy because there is not expansion so it zips right through with most of it's energy going into the ground. A 45acp has much less energy but will most likely deliver all it's energy into the animal as it won't pass through. But now take a properly designed 308 bullet and see the terminal results.
I think the point of this thread is that a 32 or 380 is not a good self defense round. And while anyone with half a brain would prefer something much larger for self defense but carrying a 1911 is not always a viable option and I would prefer to carry a 32 or 380 (or even a 22) as opposed to carrying nothing at all.
