8mm - If you plan on refinishing the stock, I would go to Wal-mart and get yourself a can of eez strip (in the paint dept). That should get off all the old finish - you can use a toothbrush for the checkering. Let it dry good then rub down with 00 steel wool.
To reseal the wood, you can use either clear Polyurethane of a colored version - lightly sanding between coats. 2 or 3 coats should be sufficient. Be sure to reseal the barrel channel.