Rifle Cartridge Primers:
Primers directly affect accuracy more than most people or reloaders realize. The primer is the only component in a cartridge that sets off a chain reaction of events. The first thing that the primer does is start the bullet moving out of the cartridge case and at the same time it ignites the powder charge which in turn pushes the bullet out of the barrel.
Some of the things that can dictate a certain primer usage are extremely hard or soft bullets, bullet seating depth, powder selection by burn rate and or amounts of powder used in the case.
Rifle primers are not the same by any means, there is a difference in the length of time which primers burn. Primers can be selected by heat or pressure range of which there are three.
Always keep in mind that between class a and class c primers there can be a hi-lo pressure difference of approximately 12%, if working at the high end of a cartridges pressure if you change primers change the powder charge as well.
1. Large Rifle Primers
Class A Large Rifle: Federal 210, Remington 9 1/2 primers will generate about 6% less pressure than class b primers and are well suited for faster igniting rifle powders like IMR 3031.
Class B Large Rifle: CCI 200 primers are well suited for medium range burning rifle powders like IMR 4320.
Class C Large Rifle: CCI 250, Federal 215 primers will generate about 6% more pressure than class b primers and are well suited for slower burning rifle powders like IMR 4350.
Note: Small rifle primers do not have a great a heat range variance as do large rifle primers but there are still three different pressure levels or heat ranges.
2. Small Rifle Primers
Class A Small Rifle: Remington 6 1/2
Class B Small Rifle: CCI 400
Class C Small Rifle: Federal 205
Just remember when it comes to custom handloading of rifle cartridges there is nothing cast in stone, it is all a matter of trial and error for each individual rifle.