Historically, rottenstone was used by soldiers to help maintain their weapons. Put a cloth over your finger, dip it into a little water or oil, then dip a little rottenstone out of the tin and rub down the metal on your musket. Made from finely ground limestone and diatomaceous earth, rottenstone is a gentle abrasive that will take surface rust off your gun barrel and lock plates. Have this on hand the next time you wake up at a reenactment and find that your barrel has turned orange overnight. Every cartridge box needs a tin of this in the utility pouch and a 1/2 ounce tin is just the right size.