I have always used just one primer for all my loads. From .338 and down to the 7mm/08 and that is the CCI BR2 ( bench rest primer)

An old friend of mine who had forgotten more about loading that I will ever know and held three world records for long rifle explained the BR2 to me.

They are hand selected for uniformity...ie the height of the anvil in the primer cup , hence the couple of bucks more a pkg. But what they do is have a longer burning ignition flame or briecence (sp) What this does is ensure a more uniform ignition of the powder for a longer period of time, also ensuring that all of the powder ignites.

My .338 would not print a decent group, no matter what I tried, from bedding to free floating the barrel and many different powders. He suggested I try a BR2...the rest is history and I have never gone back to any other primers period. With the BR2 , I have never found a need for a magnum primer.

I no longer have my .338 ( obvious by my handle) but the BR2 has NEVER let me down, or failed to print a good group.