It's a neat idea, but here are a few points to consider:
There's a good chance it would feed OK. It should be easier to get a 25 caliber bullet to fit in the "funnel" of a 357 chamber than a 357. But you'll never know till you try it.
There's a snowball's chance of getting Ruger to chamber it or Winchester to make more ammo. As a factory offering the 256 is dead. You're going to have to make a custom 25 caliber barrel.
It's also going to be hard to find an appropriate bullet. Hornady, God bless 'em, lists a 60 grain FP but like many of its more exotic offerings it's on "temporary suspension". I suspect you might run into bullet length issues with any heavier spitzers.
Best of luck and keep us posted.
