Rimfire ammunition

A rim-fire (or rimfire) is a type of metallic cartridge used in firearms where the primer is located within a hollow circumferential rim protruding from the base of its casing.

The .22 Long Rifle rimfire cartridge, introduced in 1887, is by far the most common ammunition found in the world today in terms of units manufactured and sold.

[3] Rimfire ammunition is so named because the firing pin strikes and crushes the base's rim to ignite the primer.

Rimfire cartridges are limited to low chamber pressures because the case must be thin enough to allow the firing pin to crush the rim and ignite the primer.

Modern rimfire cartridges use smokeless powder, which generates much higher pressures and tend to be of .22 caliber (5.5 mm) or smaller.

American firearms manufacturer J. Stevens Arms & Tool Company introduced the .22 Long Rifle cartridge in 1887.

[13] New and increasingly popular, the 17 HMR is based on a .22 WMR casing with a smaller formed neck which accepts a .17 bullet.

The .17 HM2 (Hornady Mach 2) is based on the .22 Long Rifle and offers similar performance advantages over its parent cartridge, at a significantly higher cost.

Special smoothbore shotguns, such as the Marlin Model 25MG "Garden Gun" can produce effective patterns out to 15 to 20 yd (14 to 18 m) using .22 WMR shotshells, which hold .125 oz (3.5 g) of No.

Shotshells will not feed reliably in some magazine-fed firearms, because of the unusual shape of some cartridges that are crimped closed at the case mouth, and the relatively fragile plastic tips of other designs.

Schematic of a rimfire cartridge and its ignition
Comparison of centerfire and rimfire ignition
Fired rimfire (left) and centerfire cartridges. A rimfire firing pin produces a notch at the edge of the case; a centerfire pin produces a depression in the center of the primer.
6 mm Flobert or .22 BB Cap ammo with Container
.41 Swiss rimfire cartridge
.22 Long Rifle – subsonic hollow point (left), standard velocity (center), hyper-velocity "Stinger" hollow point (right)
.44 Henry rimfire cartridge
9 mm Flobert shot, 9 mm Flobert shot, .22 Long Rifle shot, .22 Long Rifle, .22 Long Rifle shot, .22 CB Short, and 9 mm Flobert BB cap
Rimfire ammunition, from left to right, .22 Short , .22 Long Rifle , .22 WMR , .17 HM2 , and .17 HMR