Also picked up 3 12rd mags (.357sig 12rd mags) for the XD40 (which I also figured out last week will fit 9 .45GAPs and fire at least my target rounds). I got a couple Pierce "+2" extensions, and they fit +1 .40 and +0 .45s At least I can't get another .45 in it without a speed loader.
Some measurements that I thought were interesting...
The opening at the top of both the .40 and .357 mags is approx 3/8"
The opening at the top of the .45 GAP mag is approx 7/16"
I tried putting .40s in the .45 magazine and about 4-5rds into it the spring was too much tension and they came out through the opening.