Lee Carbide Factory Crimp Die sizes the cartridge while  being crimped so every round will positively chamber freely with factory like  dependability The adjusting screw quickly and easily sets the desired amount of  crimp. Trim Length is not critical so this extra operation takes less time than  it would if cases were trimmed and chamfered. A firm crimp is essential for  dependable and accurate ammunition, as it eliminates the problems of poor  ignition of slow burning magnum powders.