Hi, I have several bricks of Remington Thunderbolt 22 ammo. It seems pretty accurate in several rifles and a Ruger MKII pistol. Some of the boxes are over ten years old and the bullet heads now have a hard light gray (lead oxide ?) coating on the lead. This coating seems like it could be hard enough to abrade the bore of a gun as it feels little like fine sand. I have never heard of anyone mentioning this problem in the 20 years that I have been interested in shooting. Can anyone tell me if if is indeed going to damage a barrel? Thanks!