|Rimfire ammunition primarily differs from centrefire ammunition because the cartridges are not reloadable. They do not have a central primer in the end of the case, instead the rim of the cartridge contains priming compound which ignites when the rim of the cartridge is struck. The following illustration shows the firing process for a rimfire cartridge.|
|Rimfire cartridges are generally far less powerful than centrefire cartridges; power ranges from roughly 50 FPE for the .22 Short upto around 325 FPE for the .22 WMR. Recoil is equally minimal and rimfire cartridges are extremely popular all over the world for both target shooting and vermin control. Their low power and noise make rimfire rounds ideal for shooting indoors at clubs where centrefire rounds are far too powerful, noisy and expensive. For example, .22 Long Rifle rounds cost around £3-4 for 50 and with a silencer, the rifle is no louder shooting than a silenced air rifle. The two newer rounds, the .17 HMR and the .17 HM2 are generally considered varmint or vermin rounds. Commercially available ammunition of both types tends to be of the expanding variety. Having said that, FMJ target rounds are starting to appear for the .17 HMR.|
|Types of rimfire ammunition|
|The illustration on the right shows the six currently produced rimfire cartridges. There are others but these are rarer and finding suitable supplies of ammunition might pose something of a challenge. Due to the diverse design and power levels of rimfire ammunition, they are suitable for everything from indoor target shooting and vermin control to outdoor varmint control. The .22 WMR is even suitable for shooting larger animals such as coyotes and fox within reasonable ranges.
|1. The .22 Short: Developed in America in 1857, the .22 Short was America's first metallic cartridge. It was originally intended as a self defense round in the first Smith & Wesson revolver. Although some pocket pistols are still made and chambered in .22 Short, it is now primarily used in rifles for hunting and target shooting. Although .22 Short rounds can be fired in rifles chambered for .22 Long Rifle, the results will lack accuracy as the shorter bullets of the Short round require a barrel twist of 1-in-20 or 1-in-24 whilst 1-in-16 is usual in .22 Long Rifle weapons. Loads for the .22 Short vary enormously but they typically produce 45-85 foot pounds energy.|
|2. The .22 Long Rifle: The .22 long Rifle (usually referred to as '.22LR') was developed by the J. Stevens Arms & Tool Company in 1887 by combining the case of the .22 Long with the 40 grain bullet of the .22 Extra Long. Widely used as a training and hunting round, the .22LR is one of the commonest cartridges and is used all over the world. Most weapon types are available chambered for .22LR; pistols, revolvers, rifles and semi-automatic rifles. The cartridges are available in four velocity bands for different uses:|
Subsonic (usually target or practise rounds): below 1,100 feet per second.
Standard-velocity (target and hunting rounds): 1,120-1,135 feet per second.
High-velocity (hunting rounds): 1200-1310 feet per second.
Hyper-velocity (hunting rounds): over 1,400 feet per second.
In the UK, most people tend to use subsonic ammunition. As supersonic bullets drop below the speed of sound, they often become unstable and thus less accurate. Subs don't suffer this problem and are usually more accurate. The lack of supersonic crack also means that with a silencer, .22LR rounds are almost silent which is ideal in a hunting situation. As with Shorts, loads vary considerably but .22LR cartridges typically produce 100-140 foot pounds energy.
|3. The .22 Stinger: Typified by the CCI Stinger and Remington Yellow Jacket, the .22 Stinger uses a slightly longer case than the .22LR combined with a lighter bullet of around 30 grains. To minimise lead fowling of the barrel at these enhanced velocity, the bullets are usually copper-washed. The .22 Stinger is marketed as a high-power hunting round although the reduced accuracy means it is actually more suited to pistols chambered in .22LR for personal defense. Pistols using .22 Stingers are also widely used by Special Forces soldiers. .22 Stingers typically produce 165-190 foot pounds energy.|
|4. The .17 HM2: The .17 Hornady Mach 2 was introduced by Hornady in 2004. It is based on the .22 Stinger case necked down to .17 and typically fires a 17 grain bullet. The bullets are a ballistic tipped full metal jacket round that is quite challenging to produce, hence the relative expense of the ammunition. The extreme speed (around 2,100 feet per second) of the tiny rounds makes it quite flat shooting and ideal for vermin control out to around 150 yards. Because the .17 HM2 was introduced after the hugely successful .17 HMR, it is proving slower to catch on as the HMR does a similar job but better. The .17 HM2 typically produces around 165 foot pounds energy.|
|5. The .17 HMR: The .17 Hornady Magnum Rimfire was introduced by Hornady in 2002 and has proved extremely popular. It is based on the .22 WMR case necked down to .17 and typically fires a 17 or 20 grain bullet. Like the HM2, the bullets are a ballistic tipped full metal jacket round although the .17 HMR is also available as a hollow-point 20 grain round suitable for tougher or larger vermin. The extreme speed (around 2,550 feet per second) of the tiny rounds makes it quite flat shooting and ideal for vermin control out to around 180 yards. The .17 HMR is approved by some UK Police forces as a fox round. I personally know people who have used it successfully at upto 80 yards, especially with the 20 grain hollow points but rounds like the .17 Remington, .204 Ruger and .223 Remington are far more suitable fox rounds. The .17 HMR typically produces around 245 foot pounds energy.|
|6. The .22 WMR: The .22 Winchester Magnum Rimfire was introduced by Winchester in 1959. Smith and Wesson actually chambered a revolver in the calibre before Winchester introduced the Model 61 rifle well into 1960. The .22 WMR is really a dual-purpose round. In America it a reasonably effective personal defense round when chambered in small revolvers. It is also an extremely effective varmint round being suitable for animals such as crows, rabbits, groundhogs and even foxes and coyotes at reasonable ranges. Even though it is a rimfire round, reloading the .22 WMR is quite popular for silhouette shooting. The standard bullets aren't heavy enough to knock over all the plates so the rounds are pulled before firing and 50 grain bullets are seated instead. This has the additional advantage of considerably increasing the accuracy of the round. In the UK it is reasonably popular as an all-round vermin round where the occasional fox may be expected. The .22 WMR typically produces around 320 foot pounds energy.|