I shoot Black Powder Rifle Cartridge (BPRC) in NRA buffalo rifle matches and we use Swiss 1 1/2 exclusively in everything from the .40-65 to the .45-90.
I’ve never tried black powder in a Colt’s SAA just because I’ve had so much Pyrodex to burn up. I shoot Goex in my Colt’s 1860 Army’s. The challenge in a black powder cowboy match isn’t accuracy, it’s keeping your guns running through the whole match without seizing up from fouling.
What are you using to compress your powder? In the Sharps .45-70 I use a compression die to compress the powder and then place the bullet on top of the compressed powder and wad with my fingers. This prevents the bullet from being deformed from seating and compressing in one step
I use a compression die when I load 45-70 but when I load .45 Colt I do not compress enough to warrant its use (in my opinion). I just use the bullet to compress as I seat and listen to the slight crunch sound as the bullet is seated the last 1/16 inch or so. That way I know I have left no air space in the cartridge.
If I every learn that I would have better results with a lot of compression in .45 Colt I would consider the compression die. I am still learning this and am open to anybody's advice.
A 'group' proves nothing, many, many groups proves what you need to know. You are asking the O.P. to spend additional money that is not necessary. The top L/R B/P shooters in this country are using Goex Old Eynesford with tremendous success,why do you want to quibble with success ?His group was better with Swiss