This well-aged discussion isn’t unlike a good scotch, it doesn’t seem to pop up much anymore. However, it is important to know the difference when it does come up. Not only that, it can be very useful to know the details of each, the ins and outs, and why they are or aren’t used for specific things.
They are entirely different in function, they each have their own pros and cons, and they are each tailored to what they perform best at. This makes each style the only viable option for its use case and purpose. Let’s take a look at what exactly the difference is in rimfire ammunition versus centerfire ammunition, and all the details you can handle.
So, without wasting any more time, let’s get right into it. Rimfire and centerfire are two different ways of igniting the charge in a round of ammunition. They are different primer ignition systems, and they each require their own specific firing pin to ignite the primer properly.
In a rimfire cartridge, the firing pin strikes the outside rim of the base of the cartridge. This ignites the primer that backs the whole cartridge. In a centerfire cartridge, the firing pin strikes the very center of the base of the cartridge so that the primer ignites and fires the round. Aside from the functional differences, there are also performance and ballistics differences that translate into the round.
While this may sound pretty complicated, it will get much simpler once we talk about the actual parts of a cartridge. The difference in rimfire and centerfire can be immediately discerned and their name is taken, from the physical location where the firing pin strikes the primer cap.
Your standard cartridge of any caliber will generally consist of four main parts. These parts are the casing, the primer, the propellant, and the bullet. The common misconception among those that do not shoot, is that the entire cartridge is fired out of the gun, when it is only the bullet that is fired, or propelled, from the barrel of the gun.
The case will commonly be made from brass, though steel cases can also be found. They are a little harder on the gun, so they are often left when brass is sold out. The bullet is in the front of the cartridge, while the primer is at the other end, the rear. Between the primer and the bullet is the propellant, or the gunpowder.
When the trigger is pulled the firing pin falls on the primer, hopefully with enough force to ignite it and subsequently the powder or propellant. When the propellant is ignited, it explodes in a controlled manner propelling the bullet forward. The bullet speed and energy can be reliably predicted by the amount of the propellant and the bullet caliber and weight.
Rimfire cartridges and centerfire cartridges are often very easy to tell apart. Once they’ve been fired there is the very plain indent of the firing pin which will be your first clue.
The firing pin on the rimfire has to smash the rim of the primer on the base of the casing, so it will leave a mark on the cartridge somewhere on the outer edge, similar to where the numbers on a clock would be.
The firing pin on a centerfire cartridge will fall right in the center of the primer, which is right in the center of the back of the case. That will leave a small hole right in the middle of the primer that is easily identifiable.
The differences in firing systems are evident when examining a cross-section of the cartridge. This also results in somewhat different performance for different rounds depending on the type of ignition system that is used.
Rimfire cartridges are able to have a much larger surface area of the primer triggering the propellant. This also results in somewhat of a lopsided explosion, with the explosion near the firing pin having more time to progress than the powder that is directly across the diameter of the shell from the pin. This is a ballistics difference that can become very significant in larger caliber projectiles.
Centerfire cartridges have the primer located in the center of the base of the cartridge case. This primer is exposed to the propellant in the case by either one hole, in the case of a Boxer primer, or two holes in the case of the Berdan primer. These holes are called flash holes, and they are what allow the small explosion of the primer to trigger the larger propellant explosion to push the projectile.
Modern rimfire cartridges are limited to .22 or smaller. There are numerous historical accounts of rimfire cartridges of up to .56 caliber or larger, though this was during black powder use.
The first and arguably the most powerful benefit to using rimfire cartridges is that they are incredibly cheap compared to centerfire cartridges. Sometimes you can find .22LR rimfire rounds for $0.05 per round or less. This is because they are far cheaper to manufacture than centerfire rounds. Rimfire rounds need a very thin brass case with a more or less flat bottom. This means they are unbelievably cheap to manufacture, so this savings is often passed onto the consumer who then stacks that savings on their ammo shelf.
Another benefit is that rimfire rounds are perfect for training and novice marksmen. They are light rounds that only cost a few cents. The limitation of smaller calibers is actually a blessing in disguise when you need to burn a few hundred rounds during training. The smaller caliber also means less recoil and more control.
They are limited to smaller calibers, often no larger than .22LR. When you grow out of the caliber range for rimfire rounds, you definitely lose out on the rimfire ammo budget savings as well. Another potential downside is that they are non-reloadable rounds. The primer is in the case, so when it’s done, it’s done. The only other common downside is projectile range, but hey, nobody is buying a box of .22 with the expectation of sending them 700yds downrange, so no big deal there.
Common centerfire rounds include just about everything bigger than a .22. You will find centerfire cartridges in .223 Remington/5.56 NATO, .308 Winchester, .30-06 Springfield, .243 & .270 Winchester, .300 Winchester, 9mm, .44 Smith & Wesson, .45ACP, and more.
They are available in just about any size and caliber you want. They also give an increase in reliability over rimfire methods. They are considered smoother since the primer is made from a softer material. They are also reloadable and are more accurate over greater distances.
The one and only downside to centerfire cartridges is the cost. They simply cannot be produced as cheaply or with as little material as rimfire cartridges, so this manufacturing cost burden is partially carried by those who buy them.