rimfirehuls

Rimfire hulls, also referred to as rimfire cases, are the metal cartridge cases used in rimfire ammunition. In rimfire designs, the primer is a chemical compound incorporated into the rim of the case rather than in a separate primer insert at the base. When fired, the rim is struck by the firing pin, igniting the primer and propellant to propel the bullet.

Construction and materials: Rimfire hulls are typically made from brass, sometimes nickel-plated; they are generally small in diameter and have relatively thin walls compared with centerfire cases. Calibers include the common .22 Long Rifle and other rimfire variants such as .17 HMR and .22 WMR; sizes vary with the cartridge.

Manufacture: The hull is formed by drawing and forming operations; the rim is engineered for reliable ignition and to contain the pressure generated by the powder charge. The rim's priming compound is applied during manufacturing and must be intact for reliable firing.

Reloadability and reuse: Rimfire hulls are not designed for conventional reloading. The priming compound in the rim makes reusing difficult, and the structural design is optimized for single-use. Some enthusiasts experiment with rimfire-to-centerfire conversions, but such practices are rare and not widely recommended.

Usage and history: Rimfire cartridges have a long history dating to the 19th century and remain common in small-caliber firearms, especially for target shooting and plinking. The rimfire design offers inexpensive manufacturing and reliability at small sizes, but limitations include limited case capacity and non-reloadability.

Environmental and disposal: Spent rimfire hulls are often collected as scrap metal or reused in crafts; they should be disposed of in accordance with local regulations.