Difference between Centerfire and Rimfire Ammo

If you have been around firearms for any length of time, chances are you’ve run across two classes of cartridges: rimfire and centerfire. If you don’t know what those mean, you’re in luck! This article will explain the main difference between the two, as well as the pros and cons of each, and why you might choose a gun chambered in one versus the other.

What is Centerfire Ammunition?

Centerfire ammunition is prolific. Most ammunition in the United States is centerfire, and most firearms are chambered for centerfire cartridges. Let’s take a closer look at what that means.

Centerfire Ammo: Definition and Design

A centerfire cartridge consists of four parts. The case is usually made of brass. Sometimes it may be nickel-plated yielding a silver color, and occasionally it is aluminum or steel (aluminum has a dull, grey appearance, and steel is usually grey or OD green). The case is the single component that holds everything else together. Propellant, what we call “gunpowder” goes into the case.

There is a large hole at the leading end of the case that holds the projectile, also known as the bullet. The bullet also serves the function of sealing this end of the case. At the rear of the case there is either a rim or an extractor groove. Both allow the case to be removed from the gun after firing. There is also another hole at this end of the case, in the center of the case head. This hole is known as the primer pocket.

The centerfire primer, much like a percussion cap, is a cup that is pressed, open end first, into this pocket, sealing the head of the cartridge. The primer contains a primer compound that is stable but sensitive to percussion. When gun is fired using a centerfire cartridge, the firing pin strikes primer. The priming compound is crushed between the back of the primer and the anvil, a component built into a primer for this purpose, and ignited. This tiny explosion creates a small flame that ignites the propellant, firing the cartridge.

Berdan-primed ammunition has two charge holes through which flame from the primer can pass. Nearly all modern ammunition is manufactured with Berdan priming. Boxer-primed ammunition has a single hole leading from the primer to the propellant. This method of priming has largely fallen out of favor, and is most commonly seen in inexpensive or imported surplus ammunition. Of note, Boxer primers can contain a salt that is corrosive to the action and bore of the firearm, though this is not always the case. It is best to do a thorough cleaning after shooting cheap, Boxer-primed ammunition, though.

Centerfire Ammo: Benefits and Applications

Centerfire ammunition is the dominant player in the ammunition world because of its much greater versatility. Centerfire ammunition, with its center primer, has much more flexibility in other case dimensions than rimfire ammunition. It can be built with a belt like the big belted magnums, for extraordinarily powerful rounds. Centerfire ammunition cases can be rimmed or rimless, making the suitable for revolvers or ideal for autoloaders.

Because the case thickness is not constrained by the ignition system, as is the case with rimfire ammunition, the sky is the limit when it comes to velocity. Velocity is a direct result of pressure; the greater the pressure the faster the bullet is pushed from the barrel, all other things being equal. This means that center fire cartridges can be diminutive, like the low-pressure, low-power .32 ACP, or high-pressure, incredibly powerful rounds like the .500 S&W or the .338 Lapua.

This versatility is widely expressed in practice. The vast majority of the firearms on the market today chamber centerfire cartridges. There are firearms in nearly every shape and size the shoot centerfire ammo. Tiny derringers, revolvers, auto-loading pistols, semi-automatic, bolt-action, lever-action, and single-shot rifles, and even heavy machine guns chamber and fire centerfire ammunition. All modern shotgun shells, including those in .410, 28-gauge, 20-gauge, 16-gauge, 12-gauge, and-10 gauge, are all center primed.

Advantages and Disadvantages of Centerfire Ammo

Centerfire ammunition has some huge advantages over rimfire ammunition. The first is power, as defined by velocity and bullet mass. Centerfire cartridges can simply be larger and operate at substantially higher pressures, and we’ll discuss the reasons for that shortly. But there are also some other advantages to centerfire cartridges.

Because of the greater power, centerfire ammo is more versatile: from shotgun shells to pocket pistols to the largest rifles in the world, you can find a centerfire cartridge that will work for nearly any purpose. Centerfire ammunition is more durable than rimfire ammunition. The larger size of centerfire ammunition also lends itself to more consistent results, and centerfire ammunition is more reliable than rimfire ammunition. With that said, let’s take a look at exactly what rimfire ammunition is.

What is Rimfire Ammunition?

The other big category of ammunition, the rimfires, shares some similarities with the bigger centerfire cartridges, but also some significant differences.

Rimfire Ammo: Definition and Design

Rimfire cartridges differ from centerfires. First, a rimfire cartridge only consists of three major components: the cartridge case, the projectile or bullet, and the propellant. All three of these serve the same function as they do in centerfire cartridges. Conspicuously, rimfires are missing on major component: the primer.

All rimfire cartridges have a rim. When the cartridge case is constructed, the rim is manufactured to be hollow. From here a small amount of wet (and thus, pliable) priming compound is dropped directly into the case. A bit is then inserted in the mouth of each case and it is spun at high speed to force the priming compound evenly into the hollow rim of the case. The case is dried, which also dries the priming compound, affixing it in place.

When a rimfire cartridge is fired the firing pin strikes the rim. This crushes the percussion-sensitive priming compound between the two sides of the rim, igniting it. This ignites the primer and propels the bullet out of the case mouth and down the barrel.

Applications and Limitations of Rimfire Ammo

Because of its interesting priming system, some inherent limitations are placed on rimfires. First, the cartridges themselves must be fairly small to ensure reliable ignition. Since the “fire” from the primer is not directed into the propellant from the center, a smaller case can become inherently less reliable. This places a limit on the size of cartridges that are manufactured using rimfire ignition.

Secondly, the hollow rim that creates a rimfire primer and is necessarily soft enough to be crushed by the firing pin limits the pressures these cartridges can handle to low-pressure loads. A .300 WinMag rimfire would blow the back of the case out, compromising bullet velocity and effectiveness, and posing a real danger to the shooter.

It is for these reasons that rimfire ammunition is limited to just a few cartridges. The most popular are the .22s: .22 Short, Long, Long Rifle, and Winchester Magnum Rimfire (WMR, or just “22 Magnum”). There are also the Hornady .17 Mach 2 and the much more popular .17 Hornady Magnum Rimfire (HMR).

Advantages and Disadvantages of Rimfire Ammo

Rimfire ammunition has some advantages over centerfire cartridges. The limited power can actually be a boon in some situations. Most rimfires have very benign recoil and limited noise compared to centerfire ammo. This makes them ideal for new shooters, the recoil sensitive, or those with weakened grip strength. The power-band in which these cartridges operate also makes them ideal for certain purposes, like hunting small game and close-range varmint hunting.

One of the biggest benefits of rimfire ammunition is its low cost. You can buy several times as much .22 LR as you can the cheapest centerfire ammo. This allows you to shoot a lot for the money. A near-exact duplicate of your carry pistol or hunting rifle in .22 LR can mean cheap training on a very similar platform.

Key Differences Between Centerfire & Rimfire Ammunition

Ignition Mechanism

The primary difference between centerfire and rimfire ammunition is the priming mechanism. Centerfire ammo uses a removeable primer in the center of the case head, while rimfire ammo is primed off the rim. This creates a lot of secondary differences, including caliber range and power.

Caliber Range 

The caliber range of the two is incredibly lopsided. Centerfires are available in tiny cartridges like .25 ACP, handgun calibers like 9mm and .45 ACP, common rifle cartridges like .223 and .30-30, and big bores like .45-70 Government. Even shotguns are centerfire rounds. Rimfires are very limited in their calibers, to the handful we discussed above.

This does create some practical differences. Centerfires can be much more versatile. Even a single caliber in centerfire can be more versatile because it can be reloaded. Rounds can be developed with more or less velocity, lighter or heavier bullets, or bullets to perform differently. Rimfires are limited to factory options, and occupy only the lower end of the power spectrum.

Power and Performance

Centerfire ammunition will always have the edge of rimfires. This is due to case size and construction; the smaller rimfire cases just won’t hold as much propellant. Even if they did, the soft case rim couldn’t contain the pressures of very powerful rounds. This means rimfires generally represent the lowest-powered firearms available. This may be beneficial in some circumstances like small-game hunting, however.

Centerfire ammunition also has a strong, well-deserved reputation of being more reliable than rimfire ammo. A firing pin strike can fail to ignite a rimfire primer. If you need ammunition for serious purposes like self-defense, it should probably be centerfire. Both can be exceptionally accurate, but there is also the issue of power and range. Centerfire ammunition simply carries more power and can shoot accurate at much longer ranges than rimfire bullets.

Choosing between Centerfire & Rimfire Ammunition

Your choice of ammunition for rimfire options will be what is available from the factory. Because rimfire ammunition is made using a completely different process (and thus, different machinery) than centerfire ammo, there are no boutique, custom ammo manufacturers – you get what the big boys give you.

The primary difference between centerfire and rimfire ammo is that they are ignited differently, but this leads to a lot of secondary differences. Rimfire ammo is power- and caliber-limited but is inexpensive. Centerfire ammunition costs a bit more but is far more versatile, powerful, durable, and reliable.

With centerfire ammunition the world is your oyster. Unless you own a gun chambered in some obscure caliber, you can probably get ammo in a variety of bullet weights and styles to perform a variety of functions – including high-performance ammo like we make here at Grizzly Cartridge.

Whether you shoot rimfire ammunition versus centerfire ammunition will depend on a lot of factors. If you already own a gun that is chambered for a rimfire cartridge, obviously you’ll shoot rimfire ammo. But if you’re considering a new rifle or handgun, you have a choice to make. We recommend consulting with some experience shooters. Discuss your needs and what you hope to get from your gun/ammo combination.