Look striaight up the line and see if there is a hole drilled in the die, leaving a burr. It is an air/oil relief hole. Is that die a Lee? They are notorious for that.
If it is a burr try polishing it as other have said. If that doesn't get, go after it with a hardened tool such as a scribe or long punch to knock the burr loose. Then polish the die.
If it is a burr try polishing it as other have said. If that doesn't get, go after it with a hardened tool such as a scribe or long punch to knock the burr loose. Then polish the die.