For SD numbers, with large primers, I've experienced better performance with 'softer' primers (cups and fire) such as Wolf or PMC large rifle primers. Very good standard deviations in velocity... Magnum primers have 'harder' fire and cups that can be beneficial igniting harder to start powders or running in semiautos with floating firing pins, and can help deter slamfires.
I use regular primers with large rifle primer cartridges, and use magnum or military primers in semiautos. Small rifle primers I use CCI 450s exclusively, just because I got a deal on a million of them, and they work great.
Main thing is work up the load with that given primer and don't switch unless you work back up.