The Hornady Gas Checks are a great way to increase the performance of your cast bullets. The copper gas checks crimp onto the base of your cast bullets, and protect them from hot gases and deformation. The gas checks also aid in the reduction of fouling, by reducing the amount of lead build-up in the barrel. Note: Gas checks will work on either pistol or rifle bullets for that caliber. When the gas checks are seated they will be sized down to the appropriate dimensions for that bullet