Different design philosophies. There's only just so many ways of skinning the ballistic cat. Powder charge is constrained by case volume. Lighter bullets give higher velocity and smaller caliber have less drag. But they also shed that velocity/energy faster, where heavier bullets have more inertia, but greater frontal surface area, therefore more drag. All of this represents an attempt at greatly simplifying a subject that has been at the heart of firearms research since the very beginning. The desire to deliver a useful amount of energy to a target and doing a useful amount of damage at a useful range. The search for the "magic bullet" continues apace. The terrain is strewn with the corpses of cartridge designs. The original 10mm Auto load was a .40 caliber, 200 grain bullet at about 1,200fps. Another attempt to square the circle. I had one of the first of the Colt Delta Elite pistols and noticed frame rail cracks appearing all to soon. It is a powerful round that flat beat the shit out of auto pistols at the time, as the FBI found out with the S&W 1076. But it also had the unfortunate characteristic of being too powerful for female agent candidates to qualify with at the academy. https://en.wikipedia.org/wiki/10mm_Auto