I have a USP Tactical .45 and want to purchase 12rd mags for it but I am unsure which ones I should purchase. I have searched and found there to full size USP 12rd mags but I have also seen 10rd USP tactical / MK23 mags, which I have. But is there a difference in the USP tactical mags and the full size USP mags?? Do I need a mag well extender?? Where can I find 12 rd USP Tactical mags??