Rimfire Primers

Rimfire .22 LR

Rimfire ignition represents the oldest successful metallic cartridge design, predating both Boxer and Berdan systems. Instead of a separate primer, the priming compound is spun into the hollow rim of the cartridge case during manufacturing. When the firing pin strikes the rim, it crushes the thin brass against the chamber face, detonating the priming compound and igniting the powder charge. This simple, cost-effective design made the .22 Long Rifle the most popular cartridge in history. However, rimfire's limitations are significant: the thin rim required for reliable ignition limits chamber pressures (no magnum rifle loads possible), manufacturing rejects are higher, and cases cannot be reloaded since firing destroys the rim. Modern rimfire calibers include .22 LR, .22 WMR, .17 HMR, and .17 Mach 2.

Specifications

Anvil Location: N/A (priming compound in rim)
Flash Holes: N/A (rim is the primer)
Invented: 1845 (Flobert BB Cap)
Reloadability: Not possible (rim destroyed)
Availability (US): Excellent
Cost: Lowest (simple design)
Maximum Pressure: ~24,000 PSI (.22 LR)
Common Calibers: .22 LR, .22 WMR, .17 HMR, .17 Mach 2

Comparison

Feature	Rimfire	Centerfire (Boxer)
Primer Location	In rim	Center of case head
Reloadable	No	Yes
Max Pressure	~24,000 PSI	65,000+ PSI
Cost per Round	Lowest	Higher
Caliber Range	Limited (.17-.22)	All calibers

FAQ

Why can't rimfire cases be reloaded?

The firing pin crushes and deforms the rim to detonate the primer—this damage is permanent. Even if you could reshape the rim, there's no way to refill the priming compound without specialized manufacturing equipment. Rimfire brass is recycled as scrap metal.

Why doesn't rimfire ammo come in larger calibers?

The thin rim needed for reliable ignition can't handle high pressures. Above about 24,000 PSI, the rim would rupture. This limits rimfire to small, low-pressure rounds. Historic large rimfires (.44 Henry) existed but were problematic. Centerfire solved the pressure limitation.

Is rimfire less reliable than centerfire?

Historically yes, but modern .22 LR from quality manufacturers (CCI, Federal, Eley) approaches centerfire reliability. The main issue is priming compound distribution—if the rim area struck by the firing pin has thin coverage, you get a misfire. Premium rimfire has better quality control.