Using .40S&W magazines to hold 13 rounds of 9mm is very popular up here in Canada, with our 10 round magazine limits, as long as the magazine is not modified in any way.
People seem to have mixed results, and as no one who is subject to magazine limits is allowed to carry anyway, it is just for range use.
Back when I bought my BHP, I went looking for spare mags. Ken at the Firing Line said he didn't have any, but, pointed out he had .40 mags for BHP and that I could get away with an extra round in the mag. Didn't make much difference but made me giggle like an evil genius thinking, in my own little way, that I was giving the gubmint the bird.
AR pistol mags are popular as we use them in our rifles and 10 vice 5 rds per mag on the range.
Don't mean much to you guys in gun heaven, but these little victories improve our morale.
Unfortunately, the rumour now is that Trudumb is planning to announce some sweeping gun ban at a women's conf in Vancouver in June. To be acieved by Order in Council which is like your Exec Orders - no vote required. That NZ commie bitch will be there. Not confirmed yet, but we're all a little tense over it.