I used to own a 300x221 barrel that was cut for rimmed and rimless brass. I never used the 357 max brass since it needed a little trimming. I used 360 Dan Wesson brass. No trimming and it's really easy to form. You can buy it new for about $40 for 250 pieces.

Pm sent to you. FWIW you can fire rounds made from .221 brass as long as the extractor is properly fitted.
Bill