Smith & Wesson owner's manual says my 625-8 will handle .45+p. Since the chamber will be slightly longer than a .45 GAP chamber, the pressure will likely be slightly lower. Some people report loading .45 Super in their N-frame .45 ACPs. I haven't done that, and won't recommend it, but I don't think .45 GAP would be any problem pressure wise. I don't know about the accuracy though. Might deteriorate since the bullet has a slightly longer jump to the forcing cone, which distance is already long enough with .45 ACP.