above the rail 40 and protrudes away from the mainframe 20 to prevent cartridge assemblies 50 from vertically sliding off the rail 40 the distance the top plate 30 is mounted above the rail 40 is set by the type of cartridge assembly to be used as viewed in fig2 a moon clip type cartridge assembly 50 is shown as viewed in fig5 a speed loader type cartridge assembly 52 is shown top plate 30 may be attached to the mainframe 20 in an adjustable manor so that the height of cartridge assemblies 50 51 and 52 are accommodated as viewed in fig1 and 3 a propelling spring 70 a right spring follower 80 and a left spring follower 81 fit around the rail 40 and serve to push the cartridge assemblies 50 toward the right bulkhead 60 or the left bulkhead 61 depending on which end the cartridge assemblies 50 are installed it is also understood that spring 70 and the followers 80 and 81 provide enough tension on the cartridge assemblies 50 to detent said cartridge assemblies against the left or the right bulkheads 60 and 61 to prevent unwanted extraction caused by running or jumping of the user also viewed in fig1.