I was shouldering my wingmaster and before i put in in my gun cabinet i wiped it down with a clean t shirt. anyway i saw at the top of the bolt when u held it in the light it looked like blue finger prints. i tried wiping it off with my shirt and didnt come off. then i folded my shirt around my finger and dabbed it with my tongue and wiped it. it came right off. I am thinking it was just manufactiring oil they put on so it doesnt rust. The t shirt happend to be blue as well? but its gone now