Magnum primers are hotter, so you need less powder to get the same kind of pressures. Getting the same pressure does not mean you get the same velocities. the pressure curve is faster when you substitute a magnum primer for a regular one when using powder that does not call for magnum primers. My advice is to use what is called for, but in these times of near impossible getting primers, you shoot what you got. Try to use a powder that takes magnum primers, but if you can't then reduce your loads to the bottom of the charts and work your way very carefully watching your chronograph and any pressure signs you may get. Be satisfied with some thing less than max listed velocity. I was using a regular CCI small pistol primer in a 22 Hornet. Every thing was good. I used the same recipe with magnum small pistol primers. Suddenly my loads were too hot - just because of the primer. Good Luck and Good Shooting
