I have a Colt New Service Target in .45 Colt, made in 1920, in very very good condition. It has always handled the traditional .45 Colt load of a 255 grain bullet at 950 FPS, but nowadays, out of deference to its age and my deep affection for this treasured heirloom, I only shoot "Cowboy" loads.
New Service guns (in good condition) are safe with any regular factory load, or reload made to a similar specification. I would never try shooting a Buffalo Bore or +P round. These revolver are much too valuable to risk.