Rimfire

A rimfire is a type of firearm cartridge. It is called a rimfire because, instead of the firing pin striking the primer cap at the center of the base of the cartridge to ignite it (as in a centerfire cartridge), the pin strikes the base's rim. The rimfire cartridge is essentially an extended and widened percussion cap which contains not only the priming compound but also the propellant powder and the projectile (bullet). Once the cartridge has been struck and discharged it cannot be reloaded, as the head is deformed by the firing pin impact.

Rimfire cartridges are typically inexpensive, due primarily to large production quantities. A box of fifty inexpensive .22 Long Rifle cartridges typically costs less than US$1.00. Premium or match-grade .22 Long Rifle cartridges, as well as less common or out-of-production rimfire cartridges (such as the .22 Short, .22 Long, .32 Rimfire, .22 Winchester Auto, .22 WMR, and 5mm Remington) can cost substantially more.

The first rimfire cartridge was the .22 BB Cap, which used no gunpowder by relied entirely on the priming compound for propulsion. Dating back to 1857, the .22 BB Cap is essentially just a percussion cap with a round ball pressed in the front, and a rim to hold it securely in the chamber. Velocities are very low, comparable to an airgun, as the round was intended for use in indoor shooting galleries. The next rimfire cartridge was the .22 Short, developed for Smith and Wesson's first revolver; it used a longer rimfire case and 4 grains of black powder to fire a conical bullet. This led to the .22 Long, with a longer case and 5 grains of black powder. The .22 Long Rifle is a .22 Long case loaded with a longer, heavier bullet intended for better performance in the long barrel of a rifle. The .22 Long Rifle is the most common cartidge in the world. While larger rimfire calibers were made, such as the .44 Henry and the .41 Remington, the larger calibers were quickly replaced by centerfire versions, and today the .22 caliber is all that survives.

Below is a list of the most common current production rimfire ammunition:

• The powderless .22 Cap rounds, including BB Cap, CB Cap, and CB Long versions
• .22 Short, used for quiet plinking and Olypmic pistol competition
• .22 Long *becoming obsolete*
• .22 Long Rifle (LR), the most common cartridge made
• .22 Winchester Rimfire (WRF) AKA .22 Remington Special *becoming obsolete*
• .22 Winchester Magnum Rimfire (WMR)
• .17 Hornady Mach 2 (HM2), a .17 caliber based on the .22 Long/Long Rifle case
• .17 Hornady Magnum Rimfire (HMR), a .17 caliber based on the .22 WMR case

A notable rimfire still in production in Europe is the 9mm Flobert, which can fire a small ball, or even a small amount of shot like a small shotgun shell. The 9mm flobert is often called a "garden gun" in the UK, as its power and range are minimal, and it is well-suited for use in gardens, where the next-largest shotgun (a .410 gauge) would be too devastating amongst the cabbages. The 9mm Flobert is used to eradicate vermin such as mice and rats, and pigeons roosting in sheds.

Another new and increasingly popular rimfire is the 17 HMR, which is basically a .22 WMR with a smaller formed neck which accepts a .17 bullet. The advantages of the 17 HMR over .22 WMR and other rimfires are its much flatter trajectory, and it is highly frangible when used with a plastic tip. The key disadvantage of the .17 HMR is cost at present at over twice the price of .22 WMR. The .22 Long Rifle based .17 Hornaday Mach 2 is even more recent, and offers similar performance advantages over its parent cartidge, but at a higher cost. While .17 HM2 sells for about US$6.00 per box of 50 rounds, six times the cost of inexpensive .22 Long Rifle ammunition, it is still significantly cheaper than most centerfire ammunition.pl:Nabój bocznego zapłonu