CCI 550 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. Some real-world shooting conditions require more aggressive initiation than provided by standard primers. Large cases, cold weather, and certain propellants often require a hotter primer flame and a longer burn. CCI Magnum primers offer you that edge, plus you get all the attributes that make all CCI primers so great. Available in 1000 or 5000 count boxes.