Primer Size
Also: Large Rifle · Small Rifle
The primer dimension a case is built to accept, large rifle or small rifle, a choice that shapes ignition behavior and sometimes load consistency.
Primer size refers to the diameter of the primer a given case is designed around, which determines the primer pocket cut into the head. Rifle cartridges generally use either large rifle or small rifle primers, and the case manufacturer decides which by the size of the flash hole and pocket. The primer must match the pocket exactly, so the case dictates the size rather than the loader.
The size influences how much priming compound is available and how the ignition flame reaches the powder column. Some cartridges are offered in both large and small primer versions of the same case, and many precision shooters report that the smaller primer can deliver more uniform priming in certain loads. For larger cases or harder-to-ignite powders, a hotter magnum primer in the appropriate size is sometimes the better match.