Guns in .44Spl, .44Mag and .445Supermag can all shoot .44Russian, which is the oldest in the family. Each successor was stretched a bit, both to hold more powder and more critically, to make sure the new more potent version won't fit in an older gun.
If you're looking for a lower-powered defensive load for a .44Mag, several companies sell "tactical" or "street defense" loads with .44Mag shells, but horsepower levels just a hair past .45ACP levels.
You can also get .44Mag "Cowboy loads" that are way down there in power, similar to mild .44Spl loads.
In both instances, using .44Mag-length shells gives you a small edge in accuracy sometimes, and makes cleaning the cylinders easier. If you shoot a lot of .44Spl you must clean the cylinder bores very well, or the longer Magnum shells will hit the crud that builds up ahead of the shorter .44Spl shell.