Hi DearSlayer357,

I will make an assumption that if the velocities are identical between the two, then the operating pressure of the .45GAP will be higher than the operation pressure of the .45ACP. That is not necessarily indicative of anything negative, as long as Glock engineer's allowed for that in the design. (And knowing Glock's reputation, I'm sure they did!)

Also there is a difference between the the profile of the rim(less) area of the new case. If you look at a close up (or blown up) comparison you can see the profile difference. I would assume there was an advantage to the "new profile" of the rear of the case in regard to functioning. Otherwise it would not have changed.

As a result of the smaller OAL the new .45 cartridge will fit and function in a smaller frame, (receiver), size than will the .45ACP cartridge. Be that either the single stack magazine configuration or the double stack configuration. Hence, a larger magazine capacity if all other things are equal.

I'd imagine that sums up the major differences. Though I am curious if the case near the head has been beefed up on the new cartridge in consideration of the increased pressures?!?

Can't think of any others, (though I am far from well informed)! I'd be curious to know myself if there are any other differences!

Dave