I did some extensive testing with the 45 Colt and found CCI 350 LPM primers and 22.1 grains IMR 4227 powder behind a Hornady 250 grain XTP to be a superb combination. Out of my Ruger Blackhawk with a 4-5/8" barrel I had 1,089 fps avg and a nice tight group. I had tried CCI 300 also and didn't see a lot of difference but that is my firearm. You need to try them both and see which works for you and start with a reduced load and work your way up. The Sierra manual recommends CCI-350 for use with IMR-4227. I would not use the mag primers with 2400.
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