By Sanjay Soni
Before we get into technical topics like the lethality of ammunition, let’s look at the basics.
A basic understanding of cartridges and their individual components is vital to any avid shooter. This knowledge plays an important part in ensuring that you’re achieving the best results.
What’s A Firearm Cartridge, & How Does It Work?
A cartridge – sometimes referred to as a round – is a fully-assembled firearm ammunition consisting of a primer, projectile, propellant, and a casing that holds it all together. These four items are known as the components of a cartridge; and are used in a variety of firearms including pistols, rifles, shotguns and automatic weapons or machine guns. They all work together to release the projectile at high velocity, through a process of expanding gasses that propel the bullet.
The 4 Components Of A Firearms Cartridge
1. Primer – this is the explosive that sets off the propellant. The primer is struck by the firing pin once the trigger is squeezed and creates a spark that ignites the propellant
2. Casing – typically made from brass or mild steel/bimetal, the casing holds everything together
3. Propellant – otherwise known as powder, the propellant is ignited by the primer and creates the gasses and energy to propel the bullet
4. Projectile – otherwise known as the bullet, the projectile leaves the firearm and travels through air towards the intended target
The complete product – all four components combined – is known as the cartridge.
Cartridge Primers: What Are They, & How Do They Work?
As we have already mentioned, the primer is responsible for creating the spark which ignites the propellant. Upon being struck with sufficient force, the primer reacts chemically to produce heat which in turn ignites the main propellant charge and fires the projectile.
Without primer ignition, there would be no bang; the gun would misfire.
When it comes to centerfire ammo, there are two common types of primers, namely Berdan and Boxer primers.
Tip: once the cartridge has been fired, you can find which primer was used by looking down into the empty casing and observing either two flash holes, or one, as seen in the image above.
The Cartridge Case
The cartridge case, often referred to as brass, is the container which holds the cartridge components together. They are most often made from brass or mild steel, and in some cases even aluminum.
Brass Cartridge Cases
Steel Casing
Brass is the alloy of choice when it comes to higher-end cartridge cases, particularly those used for precision shooting. Brass is a highly malleable alloy, expanding rapidly to provide a gas-tight seal within the chamber when firing the bullet and then contracting to allow the casing to be extracted in the very next instant. It is also soft enough to allow for longer barrel life; reducing throat erosion when compared to other casings such as mild steel.
Some manufacturers produce higher quality brass than others. Higher quality brass results in better accuracy and a longer barrel life-span when used during reloading.
Other manufacturers such as those who most commonly cater to the Ak market sell cheaper ammunition options with mild steel casings. These steel casings are sometimes coated with lacquer to prevent rust, and are often mistaken for brass.
Steel casings are nearly 50% harder than brass casings, increasing throat erosion to a point where a rifle’s throat can be spent after only half of its expected lifespan.
Though appearing cheaper in the short term, steel-cased ammo is best avoided on high quality weapon systems with tighter tolerances.
Cartridge Case Design
Case
Case
Cartridge cases usually come in two types – bottleneck cases or straight-walled cases.
Bottleneck cases are most commonly found in rifles and machine guns, though there are some exceptions to this rule. Straight-walled cases are mostly found in pistols and revolvers.
Types of Case Rim
At the base of the cartridge case we find the rim, which provides a lip for the extractor to engage, and in many cases also serves to headspace the cartridge. Upon close inspection of various cartridge cases, you will come to notice that there are 2 types of case rims commonly used – with each serving their own purpose.
Rimmed – Sometimes referred to as the flanged cartridge, this is the oldest type of cartridge case. The rimmed case has a rim that is larger than the base. The protruding rim is used to hold the cartridge in the chamber of the firearm.
Under the metric cartridge designation system, a capitalised “R” added at the end of the designation indicates a rimmed cartridge. For example, “7.62x54mmR.”
Rimless – on the rimless cartridge case, the rim is of the same diameter as the base, and there is a gap between the rim and the body of the cartridge known as the extractor groove. Since there is no protruding rim, the cartridge must headspace on the case mouth for a straight-walled case, or on the case’s shoulder for a bottleneck case. The lack of rim makes feeding from a box magazine very smooth.
Headspace is one of the most critical measures in your rifle, and is defined as the distance from the face of the locked bolt to a datum line or shoulder in the chamber that stops forward movement of the cartridge.
Smokeless Powder: Modern Firearms Propellant
The propellant used in the majority of firearm cartridges today is known as smokeless powder. This propellant produces only a negligible amount of smoke, in comparison to black powder. The combustion products of smokeless powder are mainly gaseous and produce very little smoke when fired from small arms. In fact, smokeless powder is capable of producing six times more gas and pressure than black powder.
While the term gunpowder is still widely used, it actually refers to the outdated propellant known as black powder that is used in fireworks and antique firearms, but not in most firearm cartridges in use today.
Smokeless powder is a highly combustible single based propellant – namely Nitrocellulose – which has a clean and equal burn rate, and is typically sold in one of three different shapes. The size and shape of the propellant grains can increase or decrease the relative surface area and can significantly change the burn rate of the propellant. This allows the burn rate to be controlled. Additives and coatings can be added to the propellant to further modify the burn rate.
Smokeless Powder Shapes
Ball Powder
Also known as spherical powder, this propellant shape is faster, easier, and cheaper to manufacture. It is often rolled or flattened slightly to enhance loading density and combustibility. Ball powder feeds best through a powder dispenser, allowing for more accurate loads when hand-loading bulk ammunition.
Ball powder offers better shelf life than other powder types, and its lower burning temperatures may assist in extending barrel life. However, its way of starting with a large pressure spike and weakening as the powder burns up is not ideal for precision loads.
Tubular Powder
Otherwise known as extruded or stick powder, tubular powder comes shaped like small cylinders and is popular for use in rifle cartridges. It’s difficult to measure consistently when fed through a powder dispenser, and is best measured manually.
Mostly stick powder burns hot, which may increase barrel wear when compared to other powders, but it produces the highest level of shot consistency and accuracy which is vital for precision rifle loads.
Flake Powder
Flake powder comes in the form of flat, round flakes or disks, and is commonly used in lower-velocity handguns and shotguns. The powder produces inconsistent loads when fed through a powder dispenser, but thanks to the very high nitroglycerin level, it features superior cold temperature performance vital in some shotgun loads.
Small Arms Projectiles
Bullets come in many different shapes, sizes and weights, each specifically designed to achieve specific results during free-flight and upon impact.
Projectile Weight: When referring to the mass or weight of a projectile (the bullet head itself), we use grain as a measurement. A grain is a very small unit of measurement whereby 437.5 grains is an ounce, or 15.43 grains is a gram. For example:
• A 55gr .223/ 5.56mm bullet weighs 55-grains, 0.125 ounces, or 3.5 grams
• A 168gr .30cal bullet weights 168-grains, 0.38 ounces, or 10.9 grams
The heavier a projectile, the more stopping power it will typically retain. Heavier bullets also travel further and are generally capable of flying truer when crosswinds are present. The lighter bullet on the other hand will produce higher velocity and a flatter trajectory, which can also be advantageous.
As the shooter, it is your job to determine which bullet weight is ideal for your intended use.
Projectile Shape: All bullets are not the same. Even if some may look similar, or have similar specifications, they are all in fact very different from one another. There is a huge difference between different bullet brands, types, powders, and loads, even if the bullets you are using are of the same weight.
Even bullets of the same weight, shape, size and load from different manufacturers may have completely different trajectories. Two very distinctive characteristics that differentiate one bullet from the next – aside from weight – is the shape of the projectile’s base and tip, along with the presence or a cannelure, or lack thereof. The base is found in one of two shapes.
Flat Base Projectiles: Differentiated by the obvious flat base, these bullets have a number of advantages when engaging targets at closer ranges. The design of the flat base bullet is inherently more accurate and is often preferred amongst short range benchrest shooters. The shorter bullet profile of the flat base will also stabilize easier in rifles with a slower twist, and upon impact, the flat base bullet experiences less jacket and core separation.
In other words, the jacket holds onto the core better, allowing for deeper penetration with maximum weight retention. When engaging targets at further distances, the flat base design is slower, producing greater drag and more wind drift. They are specially designed to cause greater damage at close range and are commonly found in hunting and self-defense ammunition.
Boat Tail Projectiles: The outline of the boat tail bullet resembles the shape of a boat, with a thin nose and a tapered base. The design produces a far flatter trajectory, retains more energy, and overcomes wind better than the flat base bullet. The higher ballistic coefficient and superior aerodynamical shape improves wind resistance and reduces drag. Though this design offers superior performance in long range engagements, it does have disadvantages, including the bullet’s terminal performance.
Very Low Drag Bullets have an ultra streamlined boat tail design, which typically sacrifices bullet retention upon impact for superior ballistic coefficient, very flat trajectory, and great ability to overcome wind. The VLD bullet generally has a pronounced boat tail, short shank (the straight section of the bullet), and very long, highly tapered ogive (the curve of the bullet’s forward section) with a small hollow point.
The Bullet Cannelure
These are the tiny striations that can be seen (when present) on the bullet’s main body. The main purpose of the bullet’s cannelure is to allow the cartridge case to tightly crimp around the bullet in order to produce a more secure fit. In other words, the cannelure allows for an enhanced grip or biting point when seating and crimping the projectile.
So do all bullets have a cannelure? No. The cannelure is typically present in military grade ammo or ammunition that is hand-loaded for general use where the bullet may otherwise be pressed deeper into the cartridge case during rough handling. Precision ammunition generally lack a cannelure and rather has a smooth surface, as this aids in accuracy.
Crimping a case into a cannelure will increase pressure, and should be load developed & monitored accordingly.
Bullet Categories
Bullets generally fall into one of three categories.
1. Ball Ammunition
2. Expanding Ammunition
3. Frangible Ammunition
Ball Ammunition: Ball rounds, which despite their name are not spherical, and have a hard outer surface mostly made of copper with a lead core. This hard outer surface assists the bullet in retaining its shape and dimensions as much as possible after impact, while transferring the least amount of energy into the target. Ball rounds are designed for maximum accuracy and deeper penetration, which can be an advantage when engaging targets from behind cover. They are also the most likely bullets to over- penetrate a target.
Expanding Ammunition: Expanding bullets include soft-point and hollow-point rounds, which are designed to expand upon impact, increasing their diameter and therefore delivering far more energy into the target. They are also known as hunting bullets or self-defense loads. Once an expanding bullet hits a target, it can open up to twice its original diameter. This wider surface travelling through a living target creates a larger permanent wound cavity, and has more chances of passing through critical organs and nerve tissue, creating far greater damage when compared to ball ammunition.
Frangible Ammunition: Frangible ammo is far less common than ball and expanding ammo, and is often made from compressed copper powder. These bullets are designed to shatter or disintegrate upon impact of a hard surface, such as steel or bone. This eliminates any chance of over-penetration, but the bullets are still deadly when striking their intended target. Frangible bullets are most commonly used amongst law enforcement personnel for training purposes.
Cartridge Dimensions Explained
To a newbie, cartridge dimensions and naming conventions may seem confusing. This image can help understand how cartridge and bullet dimensions are defined.
• If you look at the projectile in the image above, you will notice that bullets are measured by their diameter and not by their length, as bullet length will vary amongst different brands and types. This particular .30 caliber bullet measures 7.62mm in diameter, which is equivalent to 0.30”, hence the .30 caliber
• The case however is measured by its length, from end to end. This measurement from case rim to case mouth is 51mm. The combined measurement – of the bullet and the case – give us the 7.62x51mm cartridge
• The cartridge length as a whole – otherwise known as the cartridge overall length (COL) – will vary amongst different brands and bullet types, and may be intentionally sized to suit a specific rifle & bullet combination during hand-loading
Sanjay Soni is the Managing Director of Hughes Precision Manufacturing Pvt. Ltd., India’s first small caliber manufacturer in the private sector. An MBA from the Indian Institute of Management, Bangalore, he has been involved with the ammunition industry in India and abroad since the last 8 years.