I'm wearing a little egg on my face....jumped on a super deal for a NIB Springfield XD in .45 GAP thinking it was a .45 ACP. Did the buy it now, didn't realize the boo boo til the next day when I read the ad in greater detail. Can .45 ACP casings be shortened for use in the .45 GAP? Got tons of casings, bullet, primers, hate to start over with new brass at today's cost...

My guess would be a yes, but a lot of work. The thing to do is look at both cartridge drawings and see if it is indeed only length which differentiates them.

Then I would carefully work up to whatever loading I was desiring.

Just finished a little online research.....the two are not even remotely similar. The GAP has different internal structure than the ACP and a rebated rim similar to the .284 rifle casing. Good news is there is plenty of new brass available and the bullets are still the same...

Oh, and it uses a small pistol primer also.