Enter any sporting goods store and you’ll see rows upon rows of different kinds of ammunition. Not only will you find a ton of different calibers and cartridges, but you’ll also find a seemingly endless selection of ammunition for the spectrum of shooting applications. There are endless options, with everything from small caliber plinking rounds to big bore cartridges designed to take out large and dangerous game.
Despite the countless options, all these cartridges can be divided into two types of basic ammunition - rimfire and centerfire.
How Cartridges Work
A standard round of ammunition (also referred to as a cartridge) contains four separate parts - the projectile (or bullet), propellant, primer, and case. All four components are present in every round of ammunition, regardless of whether it is categorized as rimfire or centerfire.
These components work together in basically the same way, no matter the type of ammo.
When you pull the trigger, it causes the gun’s firing pin to strike the cartridge primer. This action results in a tiny explosion that ignites the propellant contained inside the cartridge case.
This ignition causes expanding gases to push the projectile out of the case, through the barrel of the weapon, and toward the target downrange. The difference between rimfire and centerfire ammunition lies in how the primer ignition system functions.
Rimfire ammo is relatively easy to visually identify. If you see a small cartridge with no obvious primer embedded in the base, it is probably a rimfire round.
As the name implies, rimfire cartridges have the primer located inside the case rim. The weapon’s firing pin strikes the rim of the cartridge (rather than the center), igniting the primer contained inside. This sets off a string of events that ultimately launches the projectile from the muzzle of the firearm.
This off center, unbalanced ignition has some major drawbacks. First, it limits the amount of propellant charge that can be used in each round.
The charge is also limited due to the flimsy brass required to make an effective rimfire round. The brass must be thin enough to be crushed by the firing pin and ignite the primer. As a result, rimfire cartridges cannot contain the large powder charges needed to propel large projectiles without the brass case also blowing apart in the process. This limits rimfire ammo to small calibers.
Common Rimfire Cartridges
Louis-Nicolas Flobert invented the first rimfire cartridge in 1845. His invention, the .22 BB Cap (also known as the 6mm Flobert) consisted of a simple percussion cap with a projectile attached to the top. The cartridge did not contain any gunpowder. The percussion cap was the only propellant.
Next came the .22 Short rimfire cartridge in 1857. Developed by Smith & Wesson for their first revolver, the cartridge consists of a rimfire primer, a longer brass case, four grains of black powder, and a conical bullet.
After a dispute over the design of the .22 Short rimfire cartridge, Smith & Wesson changed the design slightly, elongating the case and adding an extra grain of black powder.
Thus, the .22 Long was born. The most common type of rimfire ammunition, .22 Long Rifle (.22 LR) was introduced by J. Stevens Arms & Tool Company just a few years later. This cartridge uses a heeled bullet, meaning the bullet has a narrow “heel” that fits inside the case.
.22 LR is one of the few cartridges that can be used in a wide variety of rifles and handguns. This is part of the reason the .22 LR cartridge is still in production today. In fact, more .22 LR cartridges are sold each year than any other type of cartridge, either rimfire or centerfire.
Some other common rimfire cartridges still in production today are:
- .22 Winchester Magnum Rimfire (WMR). This cartridge falls between the .22LR and the .223 Remington centerfire cartridges. It is often used to hunt varmints.
- .22 Stinger. This cartridge has the same loaded length as the .22LR, only it has a longer case.
- .17 Hornady Mach 2 (.17 HM2)
- .17 Winchester Super Magnum (.17 WSM)
- .17 Hornady Magnum Rimfire (.17 HMR). This rimfire cartridge produces higher velocities than the .22LR, but is loaded with a smaller diameter projectile.
Pros and Cons of Rimfire Ammunition
The biggest benefit of shooting rimfire ammunition is its cost. Due to its thin case wall, rimfire cartridges are much cheaper to manufacture. You can buy rimfire ammunition for just pennies per cartridge. This makes it a great option for high-volume shooting or recreational plinking. You can shoot rimfire ammo all day long and it won’t hurt your bank account at all.
Another awesome benefit of rimfire ammo is its low recoil. With that thin-walled case, rimfire cartridges are limited to small caliber, lightweight bullets. Anything too hefty or powerful would blow the case apart inside the firearm.
Modern rimfire ammo is limited to .17 and .22 caliber bullets and is loaded with small amounts of gunpowder.
(There are some exotic large caliber rimfire cartridges out there, but they are rare and hard to get your hands on.) As a result, this ammunition produces minimal recoil, making them a perfect option for young or new shooters.
Another potential drawback to rimfire ammo is it isn’t reloadable. However, because it is so cheap, this shouldn’t be a deal breaker.
The primer is located in the center of the cartridge case head in a centerfire cartridge. Instead of distributing the primary explosive material around the rim of the case, centerfire cartridges are made with that material held in a primer cup.
When the firing pin impacts the primer on a centerfire cartridge, it crushes the explosive component between the cup and an anvil. This action produces a spark that ignites the gunpowder inside the case.
Berdan Versus Boxer Primers
Berdan primers were invented by Colonel Hiram Berdan of the United States and was patented in 1866. Cartridges with Berdan primers are often referred to as “non-US” ammunition, despite the fact they were designed by an American.
The Boxer primer was designed by Colonel Edward Boxer of the Royal Arsenal in Woolwich, England. Ironically, modern American-made ammunition leans heavily on Boxer primers.
The Boxer primer has the anvil built directly into the primer cup.
The design makes Berdan primers easier to manufacture since empty cylinders can be punched out of a variety of metals, and the priming compound can be easily placed inside afterwards.
However, the design of the Boxer primer makes it easier to remove the spent primer after firing. This also makes cartridges with Boxer primers easier to reload.
Most Boxer primers are non-corrosive.
Common Centerfire Cartridges
Pros and Cons of Centerfire Ammunition
Because centerfire cartridges use a softer material for the primer, ignition is much more reliable than with rimfire ammo.
Also, centerfire ammunition can be made with thicker case material, allowing for larger amounts of gunpowder. As a result, centerfire cartridges can be loaded with larger projectiles and can produce more power and higher velocities. This makes centerfire ammunition more suitable for self-defense, big game hunting, and long-range shooting.
Summing It Up
While rimfire ammunition is far cheaper than centerfire, it has several limitations. Rimfire cartridges cannot be reloaded and are limited to lightweight, small caliber projectiles. However, the lighter recoil of rimfire ammo makes it ideal for introducing youngsters to shooting.
Most modern ammunition falls into the category of centerfire ammunition. Offering a greater variety, centerfire ammo is better suited for hunting (especially large game), personal defense, and long range shooting.
Deciding which is best depends mostly on your shooting applications. Fortunately, there are plenty of rimfire and centerfire options for the modern shooter to choose from.