A magnum primer has a pinch of powdered aluminum added, which gives a hotter flame on detonation. This results in (generally) higher pressures, all other things being equal. IF you change ANY one component in a load, revert to the starting load, and work up from there. Match primers are similar to standard primers, but with a greater degree of "reproducibility" in their ignition.
What we have here is... failure- to communicate.