I'm sure the military has something larger than a 10-round mag, and I'll be looking to snag a few and put the puny 10-rounder into my double-door, Canon® gun safe.
I have 20-round mags for my AR-10, and 30- and 40-round mags for the Class III AR-15s. I also have a 29-round mag (.40 cal) for my Glock 32/.357 SIG; its original price was $19. I paid $125 for it.
Net net: I'm gonna have stacks of mags which'll be worth a small fraction of what I paid for them. Depressing. Oh well, at least the AWB is sunsetting! That's a good thing.
I was thinking about getting a Glock 21 to replace my Glock 30 as my primary carry piece, but I think I'll just get a 15-round Glock 21 mag in September and just carry that as my second mag, for a total of 26 rounds of .45ACP on my person instead of 21.
I decided to always carry a spare mag after a friend told me her tale of four young toughs who approached her after driving past three times shouting lewdness, and her "oh crap" moment when she remembered she only had one 14-round magazine, having left her spare at home.
Predators travel in packs.
Fortunately they figured out what she was doing when she unzipped her Galco fanny pack and went to draw, and they all immediately jumped back in the car and ran.