Any factory load should be fine. Manufacturers tend to be very leary of blowing up old guns, and in calibers, like .38 S&W, where a lot of old guns exist, they try to load on the conservative side. Take another caliber, .38 Special, that has a lot of old guns, and a lot of newer guns made with better, more modern steel. They will sell the standard pressure stuff for old and new guns. But they will also offer higher presure ammo, +P, for use in the newer guns only. I am not aware of any factory +P .38 S&W.