For some people who haven’t been exposed to firearms, it can be a mystery as to exactly how ammunition works. We even see in TV and movies, some people still suffer under the mistaken belief that the entire cartridge fires out of a gun’s barrel. This article will be for those who are entirely new to the world of firearms, and would like a better understanding of the basics of ammunition, without getting getting lost in the intricacies of manufacturing, or caliber debates.
First a little bit of history. The modern metallic cartridge wasn’t always how guns operated, and came about only in the mid 19th century. Prior to that paper cartridges were used, and prior to that powder and ball had to be measured out for every individual shot. We won’t be going into pre-metallic cartridge firearms today, but given the complicated nature of preparing each shot, a self contained package of everything you need to fire is something to be appreciated.
Whether you call them rounds, cartridges, or shells, all modern ammunition shares a common basic design consisting of just four parts. Projectile (bullet), Propellant (powder), primer, and case (also sometimes called brass). These four parts come together to operate easily and efficiently in modern firearms.
image courtesy of http://ar15.com
Let’s break it down into the job of each part.
Projectile: The bullet is the part that the rest of the cartridge exists to launch. It’s a common mistake among non-gunners to refer to the entire cartridge as a bullet, but the bullet is actually only one part of the whole package, much the same as a blade is only part of a knife. The earliest projectiles fired from a firearm were rocks and arrows, but today’s bullets are usually made of lead. Lead is ideal for use in bullets as it’s very dense, and as such heavy for its size, and is soft allowing it to deform on impact and spend most of its force on one target rather than piercing through and continuing to hit unintended targets. Hollow point bullets are made to further enhance that deforming factor. Some projectiles are not bullets though. Most notably shotguns fire several smaller projectiles at once known as “shot,” which unlike bullets are spherical rather than domed or conical. Other materials bullets can be made of include copper, steel, and tungsten, but lead is so far still the ideal mix of weight and softness. Bullet technology has evolved quite a bit over the last few years and a wide variety of bullet styles are now available, but ultimately most bullets are still just a shaped piece of lead.
Propellant: Gun Powder is the next major component, and is responsible for doing the work of launching the projectile. The powder burns rapidly, and in the enclosed space of the case becomes an explosion. That explosion is directed in one direction behind the bullet forcing the bullet to separate from the rest of the cartridge, and accelerate down the barrel. Powders also continue to evolve thanks to advances in chemistry allowing for less powder to do the same job, and for powders that burn at different speeds to take advantage of different barrel lengths. The most significant advancement in gunpowder technology was the advent of “smokeless powder,” which came about in the early 20th century, and replaced the old “black powder,” that had been used for hundreds of years before then. Smokeless powder obviously didn’t create as much of a smoke cloud, but also burned more cleanly leaving the gun less dirty, but most importantly was much more powerful per volume. That means that a lot less smokeless powder was needed to produce the same amount of energy than black powder. This allowed cartridges to become much smaller, while having the same amount of power as older larger cartridges.
(Image courtesy of http://ar15.com) Two .45s. On the right the .45 log colt, a black powder cartridge, on the left the .45acp a smokeless powder cartridge. Roughly identical in power.
Whether it’s smokeless, or black powder, all propellant does the same job. It’s the very fact that this rapid combustion reaction is used to launch a bullet that gives guns the name “firearms,” Technically a gun isn’t a firearm if it launches a bullet by means other than burning propellant. For instance airguns, and, lasers, electromagnetic guns aren’t firearms. In spite of all their advances, over the centuries, guns are still using fire to throw metal.
Primer: The primer is what gets the powder burning. The primer is a tiny metal cup filled with a minuscule amount of impact sensitive explosive, and also contains another piece called the “anvil,” to help strike that explosive.
image courtesy of http://milpas.cc
Don’t get scared of the word explosive though. It’s not as shock sensitive as it may sound, and needs to be struck in a very specific way to set it off. The primer will be struck by the firing pin, which dents the back of the cup pushing it into the anvil and setting off the explosive between them. This throws a spark into the inside of the cartridge where the powder is waiting. Once this happens, the powder begins to burn and the whole firing process begins, all in a fraction of a second. The Primer is by far the most involved part of the modern cartridge requiring precise machinery and chemistry to manufacture. Prior to the advances that made these primers possible, metallic cartridges were impossible, and guns had to have an external ignition source such as a piece of flint in order to fire. It’s such a tiny piece that makes a world of difference.
In most cartridges the primer is a separate piece from the case which can be removed and replaced, but in rimfire ammunition (such as .22), the primer is actually part of the case.
Case: Also commonly called “brass” for the metal the case is usually made of, this hollow cylinder is filled with gunpowder, and open on one end to allow a bullet to be seated, and has a much smaller opening on the other to fit a primer. The case keeps everything together as a single cohesive unit, and is what makes metallic cartridges so convenient.
The case is usually made of brass, which is a malleable metal with a slick surface which can flex to help absorb pressure from firing, and easily be extracted once the round is fired. However other materials have been used including steel, aluminum, and even plastic to make cases.
Cases can be further broken down into different parts like the primer pocket, mouth, head, and rim, but that’s an article for another day.
The case by its self isn’t strong enough to contain the force of the powder’s explosion. It needs to be inside a chamber to fire properly. If a round were set off without being inside of a chamber, the case would simply split open allowing the force of the explosion to escape in all directions without launching the bullet.
Once the round is fired, you’re left with an empty case which needs to be extracted from the gun before another round can be loaded. Some people save these cases, as they can be rebuilt with powder, primer, and bullet and used again. This is a money saving hobby known as “reloading.”
When bullet, powder, primer, and case come together a metallic cartridge is born. The cartridge offers huge advantages over older styles of ammunition in that there is only one step to loading and that is to insert the cartridge into the chamber, and there’s no need to keep up with separate components needed to fire. Even single shot firearms can fire more quickly thanks to the metallic cartridge, and the dangers of loading mistakes are almost entirely eliminated.
These are the basic principles of all metallic cartridge ammunition. For over one and a half centuries, this has been the standard technology for all firearms, and while attempts have been made to replace the metallic cartridge, none have succeeded.