I'd go with a 255-260 cast SWC, also. The loads mentioned are good ones, but let me throw in yet another. This one's the favorite load of Hank Williams Jr (a noted single-action and 45 Colt expert): a magnum primer and 20-22 grains of 4227, held in with a firm crimp. There's no chance of a double charge, it doesn't have the ear-splitting blast of 296/110 and it launches at 950 to 1000 fps. Very nice load, although you may see some unburnt kernels.
I've posted something about this before but IMR4227 is a rarely thought of powder for large pistol cases but has worked well for me in various applications since 1976. Have mostly used it for mid-level loads but you can crank it on up there if you feel like it.
It shares the quality of 2400 of maintaining good accuracy from "relatively" reduced charge weights on up to max, although as you mention one will get some unburned powder granules in the mid-range loads.
I shot a Lyman #429215 (215 gr. SWCGC) in my SBH .44 using 20 grains of IMR4227 for years and years. You'd get a small pile of those yellowed powder kernels when ejecting cases but very moderate recoil and just accurate as all get out.
Currently working up loads for my 5 1/2" Bisley Blackhawk .45 using 18 and 19 grains of 4227 with a 255 cast SWC. Once again, velocity in the 900 to low 1000 fps range, low recoil (I believe due to it being slow burning powder so the recoil impulse is spread out over a few more microseconds) and this is proving to be one of the more accurate loads for this revolver.
Thanks for the mention of the magnum primer, never really thought of that before. I'll have to try that to see if it burns the powder more completely.
