I don't even own a .25 Stevens rifle. But I've read about different ways to make brass, including conversion from .17 WSM. So out of curiosity, I decided to see if it was possible.
First I had to make a simple fixture to hold the case to pull the bullet and expand the case mouth. Then a 3-step mandrel was made from a 1/4" bolt to expand the mouth from .168" to .250".
It took some trial and error, and a few wrecked cases - but I figured it out. It really comes down to annealing the case mouth thoroughly first.
The first couple cases I did, I tried to anneal them, but was concerned about heat getting to the priming compound. I didnt heat them enough and they both split. This time I filled the case with new crushed walnut media to just below the neck. This provided an insulating barrier. Then I held it at the base with a wet, folded paper towel. This helped keep the base and my fingers cool. The case mouth was rotated in the tip of a propane torch flame for 15 seconds. Then quickly the walnut media was dumped out and the case mouth, upside down was dunked into a shallow bowl of water to quench. I was careful not to let water get deep inside.
After annealing, the 3-step expander was put in the drill press, and the case into the fixture that was clamped in a vise anchored to the table. With Imperial sizing wax applied to the mandrel, it was slowly and repeatedly worked up and down until the mouth was fully expanded.
The case length came out at 1.175". The original .25 Stevens case was 1.125". So it was a simple matter of trimming it back .050" to make a perfect .25 Stevens case.
Now that I know it is possible, I may keep my eye out for a rifle