Until recently I thought all bullet shells were made of brass. Apparently you can also find shell casings made of steel. I cut down this .45cal casing, drilled holes, and fitted a piece of polished abalone shell in it. You can read more about polishing abalone here
. It especially looks cool in sunlight. Overall It has a 12mm diameter (a penny is 19mm) and cost me about 50 cents to make.