sar4937,
Magma uses a Dillon carbide sizing die, and polishes it out so it will size the whole case, which means it's a little larger in diameter than a standard sizing die. I run my brass through the Case Master Jr., and then size and deprime it. You want to lube the cases lightly prior to running through the Case Master Jr., and that makes them size even easier through a carbide sizing die. The cases are loaded into tubes, which you supply, and you can run the cases through the machine as fast as you can work the manual slide and pull the handle. It's a good workout when you do a couple thousand cases in one setting, but it sure makes the brass come out uniform.
It could be done on a regular single stage press, if you had a sizing die that was of the proper diameter. I'm sure Magma would sell you the die only, if you asked them. You would have to make a push rod for the press ram, but I think the Lee push through bullet sizing ram that fits on the press ram would probably work. You would need the ram that would fit inside the case, which would probably be a .357 ram, since you really just need something the diameter of the inside the case, where the web is flat to push on.
The Case Master Jr. pushes the entire case through the top of the die and out the bottom. In a single stage press that would be reversed, but the die could be screwed into the top of the press from the bottom and work the same way, but push up through the die instead. The mouth of the die is tapered for feeding the case, but the bottom isn't, which is why I would mount the die upside down on the single stage press.
Just be sure to lube the cases with some spray lube to reduce friction. When you're pushing the entire case through the die, the solid portion of the case doesn't compress.
While I was typing this, I thought about the Lee Factory Crimp Die. I believe if you took the guts out of the die, and pushed the case all the way through, that would solve your problem and be a lot cheaper. You would only have the carbide sizing ring, which is what you really need for this. You might give that some thought, too.
Hope this helps.
Fred