My first centerfire handgun was an 4 5/8" Old Model Ruger Blackhawk in .45 Colt, bought by my momma in 1973. It was a fine shooter. In the '90s, I bought a 4 5/8" New Model Blackhawk convertible in .45 Colt/.45 ACP.
Due to having a supply of free ACP ammo at the time, I seldom shot it with the Colt cylinder installed. It will group in the 1-1 1/2" range at 25 yards.
As another poster has said, there are two different frame sizes. The 1st .45 Colt Blackhawks were built on the .44 Magnum frame. Ruger brought back the original Colt sized mid sized frame for the .357 Blackhawk in 2005. The larger frame is capable of handling .44 Magnum level loads.
Due to having a supply of free ACP ammo at the time, I seldom shot it with the Colt cylinder installed. It will group in the 1-1 1/2" range at 25 yards.
As another poster has said, there are two different frame sizes. The 1st .45 Colt Blackhawks were built on the .44 Magnum frame. Ruger brought back the original Colt sized mid sized frame for the .357 Blackhawk in 2005. The larger frame is capable of handling .44 Magnum level loads.