I am moving back to 6mm BR after shooting 6BRA and have some brass left. Is there any issue sizing back to BR? I could find any identified issues online but thought I would ask here as well.
Its gonna be tough and I bet you'll crush shoulders or body. Fireformed brass, depending on how many times fired, is gonna be work hardened. I think that is gonna be a bridge too far.
Anneal it, lube the crap out of it, and yank the handle as hard as you can. It probably still won't work. I agree with 47guy, just sell it or keep it and buy new.