You can get 12 rounds of .40 into a factory Beretta hi-cap 9mm mag and and 12 into the 15 round Asian military mags that CDNN Investment sells. I havent tried any of the other mags out there because they are junk and not worth the money,except MecGar, I just have never had the chance to buy any of their pre-bans.
When I go to the range to shoot I'll put 12 rounds into the mags but the spring is pushed awful tight. Since Im shooting them right away I dont worry about it but I would never store them with 12 rounds in there for fear of weakening the spring and having it jam when you need it most. Since Ohio doesnt have CCW yet I can't carry but I keep 11 in the mag and one in the tube at home.
Although Ive never had one of the Asian mags jam on me I only use the factory Beretta mags for personal protection. The steel that the mag body is made of is a little thicker and I just feel safer using them.
BKVic