There are those who believe a prudent course of action would be to buy some 15 round mags from Arms-N-Ammo and store anything else away for a "rainy day". At such time as those stored mags may be needed, the last issue of concern will be mag capacity.
Naturally, doing this would be in violation of the sensible firearms laws here in the People's Republic (Motto: "Where the criminals are running the prison"), so the above is presented for demonstration purposes only.