I don't know about Rugers, but I've never been able to get my fixed-sighted Colts to shoot any bullet that's not in the ~250-255gr. range - and hit at my preferred POA - a dead-center hold. The only exception has been bullets in the 225-230gr. range that have been really loaded down to puny squib levels. I would start with your preferred bullet weight and then fool around with the volume and granulation of BP. JMO, but I'd start with FFFG if you have any.
The only BP loads I've made up for the .45C have been with FFFG. I compressed the 3F to pack in the max. amount, and these loads were pretty stout. I didn't have my chrony then, but I'm guessing that they were ~900fps with a 255gr. RNFP. They shot to approx. the same POA/POI as my smokeless loads at that ~900fps velocity, so I was very pleased with them. I do not find this load or its smokeless equivalent to be unpleasant to shoot at all in a SAA configuration.
The original BP loading for the Colt Peacemaker was 900fps+, and it was a real humdinger on the business end. They reduced that load to ~825fps when other, weaker firearms designs were introduced into the military arsenals.
If you find out that you really like BP loads in the large-frame Ruger, you can even fool with small duplex charges of SR4759 (~10% by volume) to aid in cleanup. That is exactly what I would do. This will increase pressure and velocity a bit and could be useful in lowering a POI.
xtm