There are two primer ignition systems in general use among modern bullets. They are centerfire and rimfire, and each of them has their own little niche in the shooting world. In essence, they work like this.
A centerfire round is constructed so that the firing pin strikes the center of the cartridge which ignites the primer, which itself ignites the powder charge, sending a projectile on its way.
A rimfire round allows the firing pin to strike anywhere along the rim, igniting the primer and then the powder charge, sending the projectile on its way.
Each of these primer ignition systems works extremely well, but for most applications, a centerfire round works better. Let’s take a look at the history of each to better understand their characteristics.
A rimfire cartridge was first perfected in 1845, with the priming compound spread equally around the inside of the hollow rim. In fact, the .22 caliber bullet of that era contained no powder, just primer, which made for a very weak shot. But it was proven effective and reliable, and best of all, since the cartridge was one piece, the round was moisture, dirt, and dustproof.
Perhaps the most famous use of a rimfire cartridge was during the Civil War in the Spencer repeating rifle. It fired a .52 caliber rimfire bullet that was lauded by the troops, which was impervious to moisture and had very few misfires or hang fires.
The heavy low-velocity bullet would do major damage no matter where it hit, and because the bullet was so reliable to fire, 20 to 30 shots could be fired per minute compared to the 3 shots per minute from the muzzle loaders in widespread use at that time.
There were two main disadvantages with the rimfire design. One was getting the primer evenly distributed along the bottom of the cartridge. The technique was called “spinning,” which used centrifugal force to push the primer into the hollowed-out rim.
Also, the rim had to be made of soft and malleable metal, and copper was the preferred choice here so that when striking, the firing pin could dent the rim and cause the primer to go off. The disadvantage with using copper was that high-powered loads could not be employed because of blowback.
Different metals were used to try and rectify this problem, but then a stronger spring was needed to dent the rim but that caused the firing pin to chip or break after several shots.
Since the South was short on copper, this was another reason why they could not perfect around for the Spencer’s that their troops captured, and the main reason why the South never had a repeating rifle of their own. It is safe to say that the Spencer repeater was the zenith of rimfire cartridges for higher calibers, and it is where rimfire ammunition made its mark on history.
Although invented somewhere around 1812, the centerfire cartridge was not perfected until 1855. It was essentially a muzzle loader primer cap placed in the center of a copper or brass cartridge.
Because the primer cap was added to the cartridge, the cap itself could be made of a softer metal that was easier for a firing pin to dent.
While the actual cartridge itself could be constructed more robustly.
That meant a higher-powered gunpowder charge could be added, giving bullets of all sizes a greater velocity when fired.
Initially, sealing the centered primer cup was an issue. Metal on metal did not give a watertight seal, and ammunition was susceptible to moisture that fouled the primer and powder
It was one of the reasons why centerfire cartridges were not initially adopted by the military. But by covering the base of the cartridge with lacquer, an effective water-tight seal was made, giving a centerfire cartridge bullet the same type of reliability as its rimfire cousin.
By the late 1860’s, centerfire ammunition became the standard in both handguns and rifles for .22, or larger, calibers. The classic handguns of the old west used centerfire ammo as did the legendary Winchester repeaters of that era.
The Major Differences
Although in theory a rimfire shot can be made as robust as a centerfire shot. The use of modern alloys for both the rim and the firing pin could be made to withstand a larger charge and favorably compete with centerfire calibers.
But overall the added expense would not be worth the cost. Couple that with the fact that centerfire weapons for larger calibers have become standardized.
It would no longer be worth it to manufacture a hardy rimfire cartridge and then manufacture a weapon that could shoot it.
There may be a niche market for a weapon like this, but the cost would need to be exorbitant for any profit to be made with no real gain in performance. Another major difference is that rimfire cartridges are inexpensive to make. However, they are inexpensive because they cannot be reused like a centerfire cartridge can. Once fired, a rimfire cartridge can only be recycled for the metallic content.
A centerfire cartridge can be reused several times by simply removing the primer cup and replacing it with a new one.
Granted, this two-stage shot case is a bit more expensive to make using more specialized equipment at the factory, but since it can be reused and re-primed, if someone has the know-how and the reloading tools, cost per shot can go down to pennies on the dollar for do-it-yourself reloading.
Centerfire VS Rimfire
Since rimfire cartridges have their advantages at lower power, and are relatively inexpensive to manufacture, they are most predominate at the lower calibers.
Virtually all .22 caliber shots are rimfire, and they are some of the least expensive bullets you can purchase. For targets or varmints, using .22 caliber rimfire ammunition is a very inexpensive way to get out in the field, or at the range, to shoot dozens of shots without much of a strain on your wallet.
There is one notable exception of the rimfire cartridge. The Hornady company makes their own specialized rimfire shot that is a .17 caliber bullet fitted into a .22 caliber case.
In most instances, the barrels on .22 rifles will need to be changed to accept this ammunition, but one round, called the Hornady Mach 2, needs a completely different rifle to fire it with. These bullets are made for varmint hunting, and as such pack a bigger wallop and have a greater range than a standard .22 caliber rimfire round.
Centerfire cartridges, on the other hand, are made in virtually every other caliber size. They have been adopted by the military and police forces since the late 1800’s, and the design of the primer cup has not changed much since the original invention.
Taken to the extreme, even mortars, cannons and howitzers are fitted with centerfire primers, making centerfire the most common, safest and easiest cartridges to use.
Above all else, the centerfire design allows the largest calibers to be fired with utmost safety to the shooter.
There is very little concern about blowback or misfires and sealed primer cups make them impervious to moisture, mud, dust, dirt, and virtually any kind of debris. In fact, the weapon would become fouled or unusable before a centerfire bullet would be.
The reality is that your choices are limited, not by your own preference, but by the manufacturers. A centerfire round won’t work in a rimfire weapon and a rimfire round won’t work in a centerfire weapon.
Manufacturers have already concluded, with safety very much
steering the process, that rimfires work best for the smaller .22 caliber of
bullets while every other caliber works best as a centerfire. For modern
shooters, your cartridge choices are restricted to the firearm you own.
However, if you are a collector and have one of the old rimfire pistols or rifles from the 19th century, you may still be able to find some rimfire cartridges available from that time period. Just don’t expect them to fire, what with the powder being so old, there is no guarantee.
But it is possible to get centerfire conversion kits for many older rimfire guns, the Spencer repeating rifle included, which will upgrade your gun to firing modern centerfire cartridges made specifically for the handgun or rifle that you own.