>>64115671 (OP)
10mm was came from a few different ideas. But the end result was a set of parameters the FBI came up with because 9mm fails too often.
.40 came about because they realized you could shorten the 10mm and in expanding bullets get the same result in depth and performance on different targets only giving up some expansion diameter.
40 and 10mm are neck and neck when both bullets expand and stay in the claimed desired depth on target.
If you subscribe to the school of thought that a bullet should stay in its target or have no energy when it comes out then there is no appreciable difference between 40 and 10mm when killing humans or game. A slightly larger expansion is all 10mm brings to the table.
HOWEVER if you think for yourself and want to end the target quickly then by choosing expanding ammo that most say over penetrates or solids then the 10mm out performs 40 hands down.
I can confidently say that handguns are not dealing with enough energy that an extra 100lbs is doing anything outside expanding the bullet more.
If a 40 and 10mm bullet both test out at 15" of penetration and the 10mm is .68 and the 40 is .59 total expanding diameter the difference is pretty damn negligible.
