About 1909 the .45 Colt case was redesigned, with a slightly larger rim than the original, to provide more positive function with the DA revolvers then coming into use.
Up until the last couple decades or so, the heaviest .45 Colt slugs were about 260gr.
Any of the ACP bullets can be used in the .45 Colt. Even ones without cannelures. It's a matter of loading technique, and not trying to go beyond the bullets limitations.
Some ACP bullet are/were made to go both ways.
here's a bit of a side note, you may see the term "Ruger Only" with some .45 Colt loads. It's a little confusing today, because there are now Rugers that won't take the "ruger only" load levels.
In the early 70s various handloaders began experimenting with heavy loads in the Ruger Blackhawk .45 Colt. THAT Ruger is built on the same frame size as their .44 Magnum Super Blackhawk. And it was found that the Ruger would handle loads in the .44 Magnum class. These loads became known as "Ruger only" loads, and there was only one Ruger in .45 Colt at the time.
Later, Ruger introduced the "Vaquero", which was also built on the big 44 mag size frame. They will also handle "Ruger only" loads.
A decade or so later, Ruger dropped the Vaquero, and replaced it with the "New Vaquero". (Important! Even though the names are almost the same the GUNS ARE NOT!)
The 'NEW VAQUERO" is a smaller frame gun than the Blackhawk or Vaquero, it is the same size (roughly) as the Colt SAA, and should be used with the same pressure as the Colt SAA and NOT "Ruger only" level loads.
There are a lot of tips and tricks used nowdays, loading the .45 Colt for different guns, at levels ranging from the light loads used in Cowboy Action Shooting up to .44 Mag levels (and possibly a bit beyond) is those guns capable of handling that level pressure.
Every gun marked .45 Colt is NOT able to handle every .45 Colt load combination. If you're wanting something above the original black powder speed and pressure, you need to do some research into the gun you have, and its capabilities and limits.
I've been shooting .45 Colt since the early 80s, in Ruger NM Blackhawks and later Vaqueros. Had my days of making a magnum out of the .45 Colt, and settled on one load a 250gr SWC at just a hair under 1100fps from my 7.5" gund. Works well, has a lot of "thwop!" and while it has noticeable recoil, its not so bad as to be unpleasant, for me, anyway. When/if I want more than that, I go to a .44 Mag. by choice.
Happy to answer any specific questions I can.
Both the .45s are great rounds, and are found in some of the best guns ever made. (also found in some cheap crap, too, so be sure the gun you get is the one you WANT.
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