Centerfire Vs Rimfire For The Total Beginner
A bullet comes one of two ways: rimfire vs centerfire. Most of them these days are centerfire, though the few remaining rimfire rounds remain quite popular.
A rimfire round lacks a primer in the base of the cartridge, whereas a centerfire cartridge has that little button in the center - hence the name! - and thus does have a primer that's struck by the striker or firing pin. That's the basic difference.
However, what are the differences? Basically, it's the ignition system, which we'll get into in more detail. Hopefully, you understand the difference a bit better between rimfire vs centerfire by the end, but it isn't terribly complicated. There is a good reason why centerfire cartridges are the default for more applications, from target shooting to carrying concealed and so on.
Rimfire Vs Centerfire: Ignition!
The primary difference between rimfire vs centerfire ammunition is the ignition system, specifically ignition of the primer.
Prior to the invention of the metal cartridge, powder and projectiles were manually seated in front of the breech either in the cylinder of a revolver or were manually rammed down the barrel of a rifle or musket. To set off the powder charge, you had to get a spark to the powder.
Typically, how this was done was to put a small amount of a priming powder (typically mercury fulminate) in a flash pan, with a hole leading to the powder charge. (Called a flash hole.) When the primer was ignited, it sent a spark through the flash hole into the powder charge, and it made a "pew."
If it didn't, you got - and this is literally where this phrase comes from - a flash in the pan.
A few different methods were invented to create the spark. Guns first had literal fuses (matchlocks) and eventually used a piece of flint for spark (flintlocks) until someone eventually figured out the percussion cap. Percussion caps have a dollop of primer powder. They seat over a nipple with a flash hole. Eventually, someone had the bright idea of putting the whole bullet inside a case instead of just the cap, and that's when cartridges were born.
That seems like a lot, but here we come to the difference between centerfire vs rimfire cartridges.
Essentially, a rimfire cartridge puts the priming compound inside an otherwise sealed cartridge. A centerfire cartridge has a cavity in the rim that a primer cap - basically an old percussion cap - is inserted into. That's the difference. However, this necessitates some differences in cartridge design.
Rimfire Vs Centerfire Cartridge Design
Since the difference in ignition necessitates differences between rimfire vs centerfire cartridge cases, let's go over them in a (hopefully) concise fashion.
Rimfire cartridge cases are made with space inside the rim, which is where the priming compound sits inside the case. Think of it kind of like a pastry or a dumpling; there's filling in the middle but usually a little bit of dead space by the crimp in the dough. In a rimfire cartridge, that space is where the priming compound is located.
Rimfire cartridges are made by dropping a dollop (less than a gram; it's a wee little dot) of wet priming compound into the case, and spinning it with a centrifuge or other mechanical device. As the case is spun, the primer is forced into the space around the rim. After that's complete, the propellant charge is added, the bullet is seated over the propellant and the case is crimped together and thus making a bullet.
Centerfire cartridges are a little more complex in construction, but simpler to make. Centerfire rounds have a base (the rim) with a divider between the rim and the main chamber of the case. A cavity is created in the center of the base, with either a single flash hole or double flash holes (in the case of Berdan primers) leading to the main chamber of the case.
Centerfire cartridges are assembled by press-fitting a primer cap into the primer pocket. The propellant charge is added to the case, the bullet is seated over it and the case is crimped to seal the bullet and thus completing the cartridge.
And that, children, is how freedom seeds are made.
Centerfire Vs Rimfire Advantages
If weighing the relative technical merits of centerfire vs rimfire, the centerfire design is the most advantageous up to a certain point.
Centerfire ammunition is, in a sense, better firstly for ease of manufacture. The primer is pressed into a case, powder added, the bullet seated and the bullet crimped together. Very simple, all things considered, and the round is stable.
Centerfire rounds are also safe, as a primer strike is needed to discharge the bullet. Granted, great care must always be taken with ammunition as part of proper gun safety, but the relative stability of centerfire ammunition is a definite boon.
Rimfire ammunition, however, is somewhat less stable. The construction of rimfire rounds - with a smear of primer inside the bottom of the rim - can lead to more dud rounds within a given lot of ammunition. Since rimfire ammunition is also more difficult to make - both in terms of machinery and also safety protocols - there are fewer factories and technicians capable of producing it.
In periods of high demand, shortages of rimfire ammunition can and do occur.
With that said, there is an inherent advantage to rimfire ammunition, namely that it is much easier to make rimfire rounds of very small diameter vs centerfire rounds of very small diameter. As a result, the smallest of bullets - such as .17 HMR and the .22 rimfire family - are much easier to make as rimfire rounds rather than as centerfire rounds.
Not that .17 or .22 caliber bullets cannot be made with centerfire cases, of course. They can and indeed are, but they are almost universally rifle cartridges. Some are small rifle rounds, such as .223 Remington/5.56mm NATO, and some are larger rounds necked down for a tiny bullet such as .220 Swift and .22-250 Remington, which are a necked-down 6mm Lee Navy and .250-3000 Savage, respectively.
However, very small caliber bullets are more easily made with rimfire construction.
Another advantage that centerfire cartridges have over rimfire cartridges is that rimfire cartridges typically use (or rather used) what are called "heeled bullets." A heeled bullet has the same diameter of the case. Basically, half the bullet is shaved down so it seats down into the case, but the case and the projectile have the same diameter.
Non-heeled bullets are a slightly smaller diameter than the case they are seated into. For instance, a .45 ACP bullet is 0.452 inches in diameter, but the case itself is 0.473 inches in diameter. Heeled bullets also don't seat well in tapered cartridges, so they don't work the best with rifles.
Why does this matter?
All bullets have a bit of lubricant applied to them, which picks up lead residue and other contaminants as it travels through the bore towards the target. This reduces lead fouling, and therefore allows a gun to continue operating (key idea!) for extended shooting sessions.
Back in the day, a range session meant only a few rounds! Black powder and lead bullets leave a lot of following, requiring frequent cleaning to maintain accuracy and reliability. In fact, it's common for black powder shooters and muzzleloader hunters to clean their guns by soaking them in the bathtub with solvents.
Heeled bullets - unless jacketed or not made of lead - have to be lubricated over the entire projectile, meaning the entire bullet has to be coated with a hard lubricant. On the other hand, non-heeled bullets only need a little bit of grease applied a groove (the greasing groove) located below the shoulder of the bullet, and therefore is contained inside the case.
Heeled bullets are therefore a little more susceptible to picking up contaminants during the manufacturing process or from anywhere else - handling, shipping, wherever.
The point? Non-heeled bullets are generally easier on guns, making them more reliable and longer-living. Since centerfire ammunition makers started making cartridges with non-heeled bullets...they became the dominant form in the industry.
The three most popular rimfire cartridges are .17 HMR, .22 Long Rifle and .22 Winchester Magnum Rimfire, aka .22 WMR and/or .22 Magnum.
There are some others that remain in production, however, though in smaller numbers. Target shooters still use .22 Short albeit infrequently, there are a few lots made here and there of .22 Long (like .22 LR, but weaker and with a longer case) and varmint hunters have some other rimfire rounds to choose from such as .17 HM2 (an improved .17 HMR) the 5mm Remington Rimfire Magnum (still in limited production though no guns are made for it anymore) and a few others.
Of these, of course, .22 LR is the most popular.
In the early days of cartridge ammunition, rimfire rounds were far more common. The original Henry rifle used a .44 caliber rimfire round (.44 Henry) and rimfire rounds such as .46 rimfire, .38 rimfire and .31 rimfire were commonly used in black powder revolvers that had been converted to fire cartridges as percussion revolvers fell out of popularity.
However, by the late 1800s they had become less common. The story goes that production pretty much ceased on all rimfire rounds bigger than .22 LR around World War II and basically never resumed since there was no real reason to.
The first centerfire cartridges emerged much earlier than some might think, though they were mostly a curiosity until sufficient design improvements - along with the advent of repeating rifles - made it so there was pretty much no point using anything else.
Early centerfire ammunition (though without a primer) emerged before 1820, but the first centerfire ammunition featuring a primer were devised around 1830 by a French inventor, one Clement Pottet. Pottet's first design was a paper case with a brass base. The shooter manually inserted a primer to be struck by a firing pin.
By 1855, Pottet's design had evolved to a brass base with a primer countersunk into the base, with a paper case, which would be recognizable to the modern shooter. Brass cases soon emerged along with the Berdan and Boxer primer designs (both in 1866, with the former being devised shortly after the latter) and the modern centerfire cartridge was born. Smokeless powder entered the picture at the end of the 19th century.
Rimfire Vs Centerfire Ammunition
At this point, rimfire vs centerfire is a moot point in most practical terms. What rimfire rounds remain are mostly for plinking and target practice though are also good for varmint and small game hunting.
Centerfire cartridges have some inherent advantages over rimfire from a purely technical perspective.
First, the use of a primer cap instead of a primer compound at the base of the round makes them inherently more stable and safer to store and transport. Ignition is also more reliable. Though dud rounds do occur no matter what ammunition you use, it happens a bit more often with rimfire ammunition.
Secondly, the Boxer primer design makes for easy extraction of a spend primer case and insertion of a new primer. The case, therefore, is reusable and the crafty/thrifty shooter can reload cases as many times as the case allows for it. How many reloads depends on what round you're loading and how you're loading it. A lower-pressure round such as .38 Special can be reloaded many times but a .30-06 or .338 Winchester Magnum will require new brass after a few reloads.
Reloading rimfire ammunition, however, IS actually possible. There are reloading kits out there for .22 LR that allow the handy and crafty shooter to reload, though great care is required. It's also a delicate procedure, requiring assiduity and finesse. It's time-consuming as well, so you aren't going to be making dozens of rounds in a sitting. That said, it is totally doable if you wanted to.
Fewer people handload these days, however, and the hassle of doing so relative to the inexpensive cost of .22 LR...may put some people off.