Request for Proposal to procure 57mm Target Practice (TP) Cartridges. The 57mm TP Cartridge is a 57mm, electrically-primed cartridge designed to function in the MK 110 Gun Mount (GM). The TP Cartridge... Request for Proposal to procure 57mm Target Practice (TP) Cartridges. The 57mm TP Cartridge is a 57mm, electrically-primed cartridge designed to function in the MK 110 Gun Mount (GM). The TP Cartridge consists of an inert projectile, a brass cartridge case, an electric primer, and propellant.