Small pistol primers have been used in the .45 acp for many, many years in other parts of the world. I have one in my collection dated 1954. In the U.S. they became more common during the switch over to Non-Toxic priming compound, which is made up of Diazodinitrophenol, or DDNP for short. The standard Lead Styphnate priming compound has a slower brisance than DDNP, and the higher brisance of DDNP pushed the primers out of the pockets at a faster speed, resulting in primer flow and extremely flattened primers before the pressure from the burning powder charge could push the brass back and reseat the primer. This occurs no matter which priming compound is used, but it's timed to interact correctly, and the DDNP priming compound messed up the timing. The speed of the primer backing out needed to be slowed down.
Several different cures for this were tried. Among them were 1/8" flash holes, crimped primers, and going to small pistol primers. All these worked to some degree, but since the low pressure and small volume of the .45 acp never really required a large pistol primer in the first place, some manufacturers decided it was a good time to switch some of their production over to small pistol primed brass, using both Lead Styphnate and DDNP primers. You'll find Small Pistol primed brass from Federal, Speer, Blazer, Winchester and RWS, just to name a few. A small pistol primer doesn't necessarily mean it's a NT primer. Most NT primed cases will have it in the headstamp from the factory, but I don't know for sure that all of them do.
On the practical side, you just load them both the same and I've yet to find a target that cared which primer was used, since the bullets go to the same point of aim with either size.
Hope this helps.
Fred