A 9mm center mass will stop the BG. No doubt about it. Seems a lot of folks think they will put a couple in the box and that will the end of that! (I am not discounting the fact that most 9s have a lot more rounds that the average 45.) It would be interesting to know how the reaction would be to a non-center mass shot. Is a 9 or 45 better? I am sure there is some data out there somewhere.
I really don't know, just asking the question... But I would think that the 45 would cause more ache than that 9. Just my thought.