Glad I didn't say "no 9mm owners need reply," because I think you're right. (Just kidding, about everything except the "you're right" part. My S&W 3913 is my second 9mm in 40+ years of gun ownership, and I sometimes wish I hadn't sold my 39-2 back in '74.)
The +2 Adapter
fits eight (but not all) different Mec-Gar mags, including the MGP22618, making those into MGP22620's.
I think I've seen a mention somewhere of 14-round .40 mags, but I'm not gonna confuse the issue even further with that.
I guess my main question from this is if the "12's" are really "13's," and if I could eventually convert the "low-cap" mags I have now to 15-rounders. I wouldn't feel too bad if they maxed out at 14, but I'd like both a bunch of mags and a bunch of rounds per
mag for my SHTF Kit.
Thanks for your input.