If you can cut it off square, good enough, if not, a machine shop should do it at a reasonable price.
After cutting, it needs to be recrowned, that is , smooth bevel or chamfer at the mouth.
Easiest way is to use a brass round head bolt in a drill motor with clover medium and fine valve lapping compound to smooth out and round off the sharp edge at the muzzle, a 1/4" bolt will do a .25 cal. easily.
Don