CCI Primers are continuously tested and improved. As a result today's CCI primers are more sensitive, easier to seat and more compatible with progressive and automated loading equipment than ever before. They utilize modern non-corrosive and non-mercuric initiator mixes for the cleanest burn possible. Number 41 Mil-spec primers are made to the same specifications of the U.S. Military and reduce the chances of a slam-fire. While designed for you in Military-style semi-auto rifles, they use the same data as CCI magnum primers. Note from CCI: Effective slam-fire prevention requires more than mil-spec primers. Headspace, chamber condition, firing pin shape and protrusion, bolt velocity, case condition and other factors can affect slam-fire potential.