I don't have any experience with the 25-20, but I love my .256 win mag. The first loads I tried in it were very accurate, so I didn't even do any load development. I load the 60 gr fp (hdy # 2510) and 75 gr sp.
As mentioned, brass is easy to form from 357 with no fire forming, although I am lucky enough to have acquired around 150 factory rounds in the past that I am now reloading. About 15 years ago, I also ran across two boxes of winchester virgin empty brass in a pawn shop bought them.
My barrel is a lightweight octagon barrel. The 256 does not make the barrel jump like heavier calibers do in the octagon barrel. It is fun and pleasant to shoot all day long. I have never loaded cast bullets in this one, but I think it would be fun to try something different.
Shoot Often,
Curtis