Primers are a very critical facctor in your accuracy formula, especially if you are pushing the envelope. Using a fat type case, such as the 300 WSM, 284, etc., I have been doing a primer experiment for my own knowledge based on some recommendations from Ram Shot & CCI. In several instances, just a change of primer has really had some eye opening effects. For instance, using both H414 & Ram Shot Hunter in max loads with a 284, velocity,standard deviation, and pressure have been changed to a verifyable basis. Some primers are hotter than others, not just magnum vs standard primers. For example, using a max load of H414 with a WLR primer as the starting point, everything was left the same with only a change of primer. Going to a Fed 210M, velocity increased 70 fps with a drop in pressure, and much better Sd. This was verified with several additional loads run over my Oehler chrono. In another instance, Ram Shot suggests using a standard primer in most loads under a 60 grain or so load. Approaching larger loads, experimentation is suggested. Their powders are designed to burn slower for consistency. Using too hot a primer can cause the powder to light off too fast and not do its best. Using Hunter powder in a max load in the same rifle with a different bullet, after max pressure was reached and then backed off 1 grain using a CCI magnum primer. A WLR primer,Fed 210, Fed 210M, & Fed 215 were changed with everything remaining the same. Again, pressure sign changed, velocities changed, and Sd changed. In fact, as suggested by Ram Shot, velocities were much higher (over 100 fps)by using std primers vs magnum primers. Same has held true with H4350 and several other powders in similar burning rates. Just a reference for your future load developments. Good luck.
I realized that they were all CCI 250 mag primers. The load is under max with large rifle primers that i tested before by @3 grains. 
