The barrel-maker who fitted mine altered the reamer as I requested, to make a definite stop shoulder for the mouth of the case. This leaves a definite imprint on full-length cases when I fire-form 'em with inert filler, so I know then exactly where to trim 'em back to. I don't recall how the throat is. Don't know where the chamber cast is. I'd advise as short a throat as you can get-by with.
