Some find that the same caliber in both revolvers and rifle is a good idea. I'm looking that way myself. Remember that you have to be using lead bullets and keep it under 1400 fps. Then go out and have fun.
People shoot both .44 mag and .44 Special. I shoot .44 Special for rifle and .44 Russian in pistols. The .44's are straight walled cartridges (except for the .44-40/.44WCF, a completely different cartridge) and is easier to load and longer lasting than the necked cartridges but will not serve you as well if you want to shoot black powder.
There are more gun choices in .45LC for both pistols and rifle and the rifles in .45 maybe a little easier to find and cheaper. Handle and shoot as many of the choices as you can before buying. And if you plan to be competitive then you will have to have some slicking and smoothing done to any of your guns--usually the club that you shoot with will have a favorite local gunsmith. Find one that has worked on your type of gun and check out, handle, and if possible shoot a sample his work and ask about prices. There are a dozen or more excellent gunsmiths around the US that are known and discussed on the SASS wire but plan to add about $75 for two way shipping and the time to do it if you don't find anyone local.
For the first shoot or two just come watch. Buy leather and a gun or two and you should be able to borrow a gun or two from people at your local club--at least for the first couple of matches. I recommend that you don't buy "get by" leather or hardware. If you buy the wrong stuff (unless it is quality stuff, just not right for you) at the beginning you may be stuck with it after you buy the right stuff six months later.
Don't be hesitant about cornering the top shooters at the closest clubs and asking their opinions of leather and hardware--they have all been thru it and almost to a man or woman, are among the nicest people in the club and will be glad to help you.
You can shoot 44Mag cartridges loaded down to 44Special velocities, under 100fps. about 800fps is good. Some brands of rifle don't want to feed 44Special, so you have to use the 44Mag case. 44Mag hanguns will shoot 44Mag, 44Spec, 44Colt and 44Russian.
Which is more versatile is a tossup, if it's in a Ruger. More different cartidges will fit in the 44 chamber, but the 45Colt will also chamber 45S&W (Schofield). Bullet choices are limited only by what the rifle will feed smoothly. You can also buy a 45Colt revolver with another cylinder for 45ACP from several makers. 44Mag brass is heavier and harder to take the higher designed pressures, and 45Colt resizes easier for that reason. (With less pressure on the reloading machine lever, that is). 45Colt, 44Mag and 44Special all reload easily.
44 mag is fine. There are lots of cowboy loads out there for 44. Yes, believe it or not, if you are going to buy cowboy loads 45s are easier to find. There are 44 loads (factory) for CAS but not as many. If reloading you can download the mag cases just fine. If you've got a pile of special cases use them but as noted not all rifles like the shorter cases.
So if you are going to have 2 different calibers it really won't matter. May as well have a 38 and a 44 pistol and 44-40 rifle. My point here is, it's just so much easier to have one caliber to deal with. There's more activity involved than if you are shooting 10 different types of guns out in the pasture. Most guys carry all of their stuff to the loading table at once so one caliber is easier to keep up with. No reason to say you have to have them all the same but with 44 mag and special, they are kind of close in appearance so it's not that hard to stick a special in a rifle when you are loading and jam it up. I used all magnum brass when I was shooting 44s but that doesn't mean you have to.
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