Reloading for the Mk I Lee-Metford – .303 Cartridge by Britishmuzzleloaders Military history Reloading Surplus arms No Comments 2015. June 1. Britishmuzzleloaders bring us the complete showcase of reloading the .303 british cartridge. The video covers alloys, casting, sizing, reloading, and of course: package and testing. A whole lot to learn!