I just ordered some Buffalo Bore Deer Grenades, 260gr, medium cast hp
Those look good. I read their info. BB 260's should do about what you're wanting them to do.
I got some 255 gr. Beartooth flat nose, gas check bullets, am trying near max loads of H-110, Power Pro 300-MP, Vhitavuori n-110 and IMR-4227. Burn rates are pretty close, will see how they shoot. The H-110 powder is 50-60 yrs. old, smell good, no sign of deterioration, preforms great. It came in paper bags. The bags started to crumble, powder now in used powder cans with new labels.
Out of my 24" Cowboy, I'm looking for MV's of 1,700 fps or better.
I finally found some Sierra Sports Master 300 gr. flat nose bullets. Those are some of the hardest bullets Sierra makes, terminal performance reportedly about like hard cast. At 50 yds, they shot a clover leaf group out of my Cowboy over near max load of IMR-4227. Didn't clock them, probably running around 1,500 fps. These 255 gr. Beartooth slugs will have to do pretty good to keep up with the Sierras.
A .45 Colt rifle with optimal loads isn't anything to sneeze at. It'll put a WT's nose in the dirt pretty fast, hogs, too. Just not a long range set up, mean killing machine out to around 150 or so. In the woods and over small food plots, should do well.
DF