The single stack .45 acp is the G36. But thats what I heard, that you would be better off with just hanging on to your .45 autos. The GAP is not ballistically superior in any way (despite the company claims. It is not possible to shorten the cartridge and better the ballistics) and kicks too much for the pistol it was designed for. The G37 is far too small and light, since the GAP is overloaded to try to compensate for the velocity and power loss afforded by the decreased overall height of the case. It was designed to give the user .45 power with 9mm capacity. But in my opinion, if you need more than 7 or 8 rounds of .45, you seriously messed up, my friend !