When I’m running a chainsaw, I’ll sharpen the blade after every two or three tanks of gas, depending on what type of wood I’m cutting. Even if you could position it just right to have the blade shave off small pieces of metal (and they’d be very small), they would just heat up and quickly dull. The blades would then basically be just thin pieces of metal hitting a thick piece, and the chain would fail far before the shotgun did.