The following is a starting load for 45 Auto!
Do Not Use This Load In Any Of The SAA Or Italian Replicas.
Midway LoadMAP 45 ACP, page 70:
Hornady XTP 230 grain,
Alliant Bullseye - starting load of 4.7 grains - 15,600 psi - 755 fps.
So just using light 45 Auto loads is like playing Russian Roulette in the revolvers that this case was meant to be used in. Will the light load blow the cylinder apart, will it shoot like a full 45 Colt load, or will it actually be light? Keep in mind that the revolvers that this case was designed to be used in are the original SAA and the Italian replicas thereof. The shooting discipline will not allow them to use Ruger Redhawks or Blackhawks.
The whole idea of these cases is to not only stay well within the 45 Colt max pressure of 14,000 psi, but to produce a very soft shooting round from 700 fps on down to 475 fps which can not be done at 14,000 psi, to which many more 45 Auto starting loads are rated at, which defeats the whole purpose of the case being redesigned for soft shooting rounds to start with.
Why play with fire when there is published safe load data? There is no longer any need to have to take a risk by trying iffy 45 Auto data being there is now tested and proven totally safe Cowboy 45 Special load data in the Cartridges of the World - 17th edition.
This OP is not about modern higher pressure handgun, but rather the original SAA revolvers and modern day Italian replicas thereof, which are limited to 14,000 psi. And because these lower pressure 45 Colt handguns still exist to this day SAAMI keeps the pressure for the 45 Colt at 14,000 psi. It is the safe thing to do. Now if one has a Ruger Redhawk they are reportedly being loaded upwards of 50,000psi by the Wild Bunch. Yet this would not only blow the older handguns apart but get people hurt too. Not to mention some of the modern 45 Colt revolvers could not hold together at such pressures either. And while these Cowboy 45 Special cases can handle hot loadings they should never be loaded hot in anything other than a Ruger Redhawk or Blackhawk. And the Blackhawks should not be loaded as hot as the Redhawks. Know the gun you are loading for is the key take away here.