As already mentioned, if you run the reamer into a hardened seater die you will ruin the reamer. Best solution is to make a new seater with the reamer from a die blank or a chunk of free machining steel. If you insist on using an existing die it would have to be lapped out, which would take a while and you need to know what you are doing. Might be able to open it up with a carbide boring bar and then lap, but the little bar is going to be way up in there and is going to want to chatter.
Can a hardened die be honed on a diamond hone?
Roy
