Clean the rust off as much as possible to expose how much pitting there is, then take a picture and send it to the CMPicon. If you ask them to have the armorer look at it and see what he says they may ask you to send it back. I had a Grade C receiver that turned out to have some deep pitting at the receiver ring. The armorer said that it should have been a salvage grade and they paid for me to ship it back and sent another receiver.