I am with GB on this. I use a trim die. The one Redding has is a rough sizer too. I am working with 221 FB from 223 cases. I lube up the 223 case run it into the trim die and then cut it off with a Dremel close to the die. but not touching it. I used a hacksaw, but the Dremel is quicker. I then take the case out and finish trimming with a Lee, but any trimmer will work, because you are close now. I take off the burrs, then run it into a full length sizer. I have filed them down to size, but found the lee to be quicker.