SaxonPig, just about all factory .45 Colt ammo works just great in the shorter of the two .45 Colt cylinders, so there isn't a problem here.
The Model 25-3 125th Commemorative was the first production and cataloged .45 Colt from S&W. The cylinder used is about .08"-.10" shorter than the cylinder in the Model 25-5. S&W made more of these shorter cylinders than they did guns, and until they ran out of them, you could have their service department fit one to your 1950 or 1955 .45 ACP, to have a convertible. It was the same length cylinder that S&W used for any special order .45 Colt they made before 1977.
The only "ammo length problem" you may encounter is heavy bullet boutique stuff, reloads with some cast bullets (like Lyman's 454424 SWC) and... that's about it.
The standard factory .45 Colt ammunition with the 250-255 grain conical round nose lead bullets from Winchester and Remington, the Winchester 225 grain Silvertips, the Federal swaged SWC lead bullets and various 'cowboy' factory loads all fit the shorter S&W cylinders just fine.