Springfield Armory does not make bigger magazine for the XD-40. You could take your 12rd magazines with the grip extensions and add Arrendondo or AGP magazine extensions to them and you would have 15rd magazines. I believe Pro-Mag makes a 20rd XD-40 magazine and this would work with the XD-40SC but the grip extensions would not fit well. I have read and heard that Pro-Mag also has a reputation as less reliable than the factory magazine but I have never personally own one.
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