I'll add that not all rifles chambered for 25 Stevens use a .251" groove size. My understanding is that Stevens made rifles do, at least the early ones. But Remington and perhaps others used a .258" groove size (plus or minus a little). So definitely slug the bore to find out what you have. Centerfire cases are pretty easy to make from .22 Hornet brass. Converting them to reloadable rimfire takes a bit more work. I'll say up front this is not for the beginning or casual reloader. It takes special effort and care to make these. If you are seriously interested in pursuing this, PM me with your email address. I've written up detailed, step by step instructions with photos showing how I make my .25 Stevens cases. I can send a .pdf of it.
Steve