If you do not have a dental pick set to clean carbon off of your weapon (really useful for semi-autos), take a wire coat hanger, cut off about a 4 inch piece from the bottom, straight part.   When you have the piece taken out, take a hammer and put one end on a hard flat surface, and hit it one good time.  That end should resemble a standard screw driver.  Now scrape carbon off the bolt to your hearts content.