If you want to reform brass, especially bottle neck cases, you need to start with quality brass and use quality dies, plus you always clean, anneal and size the brass before you even think about reforming the brass. No short cuts, do it right.
I studied these two cases at length before deciding to build the gun as pictured. The 25-20 started life as a necked down 32-20. However, today, the 25-20 has different set of specification for the base and body, from the 32-20. If you analyze necking the 25-20 to 30 cal, you will basically find that you get an elongated straight wall 30 carbine with a rim. I use 32-20 and 25-20 brass both to create this cartridges. I use a 25-20 FL sizing die, cut off at the shoulder, then a 25-20 FL sizing die , then a die with 308 expander ball. Basicly, I form the 32-20 all day long to a 25-20 or the reverse then into a 30x25-20.
The idea was to create a revolver that used 30 cal rifle bullets at 150+ grains and 1,700 fps to take advantage of the BC of the rifle bullets, for distances of 200 meters with the terminal momentum suffcent to take down a 70 pound T-1 ram.
Illustration of the results. With 150s to 200s, you get this, for a 308 Revolver, which I built, made the barrel and cylinder inserts from a new rifle barrel blank, the long barrel nut, long barrel wrench, reamed the cylinder chambers on a 445 cylinder, chambered the cylinder chambers, etc: