primerpocket

A primer pocket is the recessed cavity in the base of a center-fire cartridge case that holds the primer, the initiating component of the cartridge. The pocket sits at the center of the case head and is formed during case manufacture. Its dimensions are designed to accommodate a specific primer size and type, such as small pistol, large pistol, small rifle, or large rifle.

The primer sits in the pocket and, when struck by the firing pin, ignites the primer's explosive charge. The resulting flame travels through a flash hole to ignite the main propellant charge. The pocket must be rigid and correctly sized to ensure reliable ignition and proper seating of the primer.

In reloading and ammunition production, primer pockets may be uniformed or cleaned to maintain consistent primer seating depth and ignition. Tools used for this purpose include pocket uniformers, swagers, and reamers. Uniforming is common in precision or high-volume reloads to reduce variations in ignition.

There are differences in primer systems that affect the pocket. Boxer primers, where the anvil is inside the primer itself, are the most common in modern reloading and cartridges. Berdan primers rely on a separate anvil in the case and typically have two small flash holes in the pocket area, which influences pocket design and tooling. While the pocket concept remains the same, Berdan-style cases often require different handling and equipment for reloading.

In summary, the primer pocket is a critical, standardized feature of center-fire cartridge cases that houses the primer, enabling reliable ignition of the propellant when the cartridge is fired.