I have two loads for the 45 Colt: 9.0gr Unique and ANY weight bullet up to 285gr. That pushes my 270gr LSWCHP at 1000fps from my M25 -7. It will NOT shoot to the sights. I even lowered my rear sight and then some to make them shoot 3" high @ 25 yards. They cycle really well through my Puma in the same caliber. From that firearm, they are more like 1200fps though. I can tell you this, @ 100 yards or under, deadly! Not only that but that .452" bullet makes stuff move around kind of cool!
I also have several loads that give me 1300-1400fps with the 45-270SAA bullet from a Ruger Blackhawk 45 Convertible with a 5 1/2" barrel. They develop 1800fps from the Puma. All of those loads though are much outside SAAMI pressure specifications for the caliber and I won't post them here.
If you want to look them up, get a subscription to loaddata.com and do a search for 45 Colt loads. Brian Pearce wrote an article for Hanloader Magazine in #246 where he experiments with three levels of loads. 14,000psi -standard pressure, 20,000psi - modern double action revolvers such as the Smith 45 Colt models, 32,000psi - Freedom Arms, Ruger, Thompson Center and others.
The loads that develop higher than normal velocities can also be found at John Linebaugh's website. He has some REAL ZINGERS!
p.s. With the Ruger, I can get the sights to regulate to heavier bullets.
Hope this helps.