Let’s talk about … ammunition

In the cadet forces we are privileged to have the opportunity to fire a number of different weapon systems as we progress through the syllabus. Generally we start with the air rifle on a short indoor or outdoor range, perhaps also firing the paintball markers in an outdoor Close Quarter Battle lane, then move on to the Cadet Small Bore Target Rifle (CSBTR) before training and spending the majority of our shooting career on the Cadet GP Rifle. At the top end of cadet shooting, is the Cadet Target Rifle (CTR), and we may also have the opportunity to fire shotgun. What all of these weapons have in common, is ammunition.

This article is part of your continuation training, and aims to broaden your military knowledge and introduce some engineering and scientific principles that you may wish to research further or introduce as examples in coursework. This article will not look at air rifle pellets, paintball pellets or shotgun shells, but will focus on rifle ammunition.

Currently, the limit of your knowledge regarding ammunition most likely comes from Cadet GP skill at arms lessons, mainly Rifle Lesson 3 Basic Handling Drills. For this, we are taught that we have “3 types of ammunition available:

• Drill – Either a silver coloured grooved case and a copper jacketed bullet, or a solid machined single piece round all silver in colour neither of which have a percussion cap. 
• Blank – This round has an extended smooth brass case but no bullet. The top of the case is closed by crimping and there is a percussion cap in the base. 
• Ball – This has a smooth brass cartridge case, a jacketed bullet with a percussion cap in the base.”

And in the lesson we are told to “always look after ammunition, keep it clean, dry and free from oil. In addition:

1. Never let it lie in the direct rays of the sun as this can cause inaccuracies. 
2. Never use a round as a tool. 
3. Tampering with ammunition is dangerous and is forbidden. 
4. Damaged rounds are not to be fired and should be handed into an adult instructor. 
5. Magazines are to be inspected regularly. Damaged magazines will cause stoppages.”

But to really understand ammunition and in order to broaden our knowledge, let’s go deeper into the subject.

Remember, at the end of each exercise or range period you give a declaration stating you are not removing anything. This is against cadet regulations and you could be disciplined for doing so. Live ammunition is illegal to possess without a licence. You must not remove anything from a cadet or military range.

Terminology

There is some terminology we use in the Cadet Force that is worth clarifying before we begin.

• Small bore – Typically ammunition up to and including .22″ which in our world is the CSBTR.
• Full bore – Anything above .22″ meaning 5.56mm Cadet GP and the 7.62mm CTR.
• Live – A round of ammunition with a primer, propellant and bullet. Should not be used for ammunition that has not been fired, as this can also include blank ammunition.
• Unfired – A round of ammunition, either live or blank for which the primer has not been struck and has not been fired.
• Misfire – A round of ammunition, either live or blank for which the primer has been struck but has not functioned.

Identification

Before getting into the technical depths of ammunition design and construction, there is one identifying feature on all issued ammunition that will help us to identify the ammunition; this is known as the headstamp.

At the base of each round will be stamped a number of pieces of information giving us information such as:

• Ammunition designation
• Date of manufacture
• Manufacturer
• NATO standard

As you notice, the larger the base of the round, the more information that can be stamped. Starting on the left is a 7.62 mm cartridge case, and it contains 4 pieces of useful information for identification.

• L46A1 is the designation of the complete round. We know from researching the designation online that this was used for ball ammunition.
• CBC is the manufacturer. This stands for Companhia Brasileira de Cartuchos, and is one of the largest ammunition manufacturers based in Brazil.
• 09 is the date of manufacture – 2009.
• Finally is the NATO cross, this symbol (+) is included in the headstamp of all ammunition that is manufactured to the required NATO standard.

Another interesting feature is the green lacquer that is used around the primer cup. This is known as the annulus and tells us what bullet was fitted to the cartridge. A green annulus of this era indicates a ball round.

Moving along are two 5.56 mm cartridges, the first being a case from a live round, and the second from a drill round. While there is no designation due to space restrictions, we can see the round was manufactured in 1988, it is NATO standard and was manufactured by RORG (Royal Ordnance Radway Green). The purple annulus seen around the primer indicates this was a ball round. The drill round was also manufactured by RORG, a year later in 1989.

Finally is an example of a .22 inch rimfire round such as those fired in the CSBTR. While not military ammunition, and with no space for a full headstamp, the E simply indicates a manufacturer – Eley.

We are also probably able to visually identify a type of ammunition, and it is from this initial visual check we can start to see some differences. Below is a visual comparison; on the left is a single .177″ air rifle pellet, made from lead, next is a .22″ ball round for the CSBTR, with the bullet also made from lead. The two larger rounds on the right are 5.56mm and 7.62mm his velocity rounds for the Cadet GP and CTR weapons. Compare the size difference, and considering the cartridge case (the brass cylinder) contains the propellant, there will be much more energy on the right of the image that for the round on the left. It’s also no coincidence that there is a metal jacket around the lead core of the bullets with the most kick. Later on, we’ll explore why this may be.

Ammunition Construction

A ’round’ of ammunition as it is often described as, consists of 4 main components. A failure in any one of these will result in a performance failure of differing proportions, however when it comes to the accuracy of the ammunition, the projectile design is most important, with propellant.

1. Cartridge Case
2. Propellant
3. Primer
4. Projectile

So what does each component consist of or do? Let’s break it down and have a look.

Cartridge Case

Something we consider as being disposable has quite a large role to play in firing a weapon system. The cartridge case not only has to hold the propellant and protect it from moisture, but also has to hold the ignition system (primer), retain the projectile, protect the propellant from ignition when sitting in a hot chamber waiting to be fired, but it also has to create a gas tight seal to prevent any gas escaping rearward when the propellant is ignited; this final stage is called obturation. To achieve this, an alloy called ‘cartridge brass’ is generally used, made from anywhere between 80:20 or 70:30 copper zinc (that’s between 70-80% copper and 20-30% zinc). This material is soft enough to allow the cartridges to be manufactured by drawing out (or stretching) the case from a solid disc of cartridge brass. It can then be swaged (moulded) to achieve precise dimensions and annealed (heat treated) to change the hardness to varying degrees along the length of the case. Let’s look at the anatomy of a cartridge case.

Starting at the base of the cartridge case is what as generally referred to as the rim. This is a bit of an inaccurate name, as both the 5.56 and 7.62 ammunition used by Cadet Forces are rimless, however old rifle ammunition contained a rim, so the term has stuck. If you look at the .22 ammunition used in the CSBTR, it is rimmed. What our example above does have, is an extractor groove. It is this groove that the extractor on the face of the bolt grips to remove the case from the chamber.

Moving on to the body, and there is little of note here, other than the varying wall thickness. The bottom of the cartridge body will be thicker and stronger, and towards the neck of the cartridge the thickness decreases. It is the neck of the cartridge that fits into the barrel extension, and this part must be stiff enough to hold the projectile in place during storage and normal carriage in a magazine, but soft enough to expand to let the projectile leave when fired.

The length of a cartridge case is used to supplement the description of ammunition in order to avoid confusion between different rounds of the same calibre. For example, 7.62mm is a common ammunition type. It is also known as .308 in the civilian shooting world. Just using the calibre is not enough to ensure we have the correct ammunition. However, the cartridge length gives us a complete description, which for a 7.62mm NATO cartridge is 51mm, and for a 5.56mm NATO cartridge is 45mm. So, this now gives us correct descriptions of 7.62x51mm and 5.56x45mm. What about that .308? Well, the .308 Winchester (or .308 Win) cartridge is manufactured to the same standards as the NATO 7.62x51mm, so provided the correct designation is used, then you may have transferable rounds.

Did you know that Soviet bloc countries have two sizes of 7.62mm cartridge, and neither were the same as the NATO 7.62x51mm? Thats right! The 7.62x39mm or 7.62 Short is the ammunition used in assault rifles such as the AK series, and the 7.62x54R or 7.62 Long is a rimmed round used in light machine guns like the PKM or sniper rifles such as the SVD.

Without including the cartridge length in the description, we could end up with the wrong ammunition!

Propellant

Someone once told you it was gunpowder? How dare they! Although technically any form of powder used in firearms could be classed as a ‘gun powder’ the term probably makes us think of black powder – the old charcoal and saltpetre mix used in canon and muskets. Modern propellants are an exact science that have progressed since the days of gunpowder. Not only do they have to provide sufficient volumes of gas and pressure to fire the round, they have to burn at a sufficient rate to expel the round from the barrel, but not too much or there will be energy wasted. Too little gas produced and the barrel friction will slow down the round, even getting it stuck in the barrel. But if it burns too slowly, the desired velocity won’t be achieved; but burn too quickly and the breech could explode. Adding to the problem, the more heat and pressure that is generated, the faster the remaining propellant will burn. A mathematical and chemical conundrum, the exact science I won’t cover here. All of this with a minimum of smoke and flash; we don’t want to give away our position do we?

And why can’t we leave ammunition in direct sunlight? Because raising the temperature of the propellant can cause the reaction to speed up, raising pressures and velocities, normally resulting in inaccuracies, but in extremes this could cause a failure of the chamber or barrel.

Modern military propellant is one of two varieties; single based or double based. Single based propellant uses nitro-cellulose (NC) as the main ingredient and are found in the British manufactured 7.62×51 ammunition. Double based propellant, consisting of nitro-cellulose and nitro-glycerine (NG) burns hotter and can deliver higher energy than a single based propellant, and is the propellant of choice for our 5.56×45 ammunition.

During manufacture, the propellent is extruded into tubes, and then cut into tablets. This is done when the propellant ingredients are a paste, and it is then squeezed under pressure through a die, just like a sausage machine, to create the tubes that are cut to size as they are extruded. As well as tubular propellant used in UK ammunition, spherical (balls) are common elsewhere in the world.

The rate at which a propellant burns is key to the performance of the ammunition. To moderate and control the burn rate, some propellants have internal voids or holes to increase the burning surface area. Given that burning will only take place on the outer surface of a grain of propellant, being able to control (and increase) the surface area of the grains is an advantage. Manufacturing internal voids, holes, or even creating star shape grains will all increase the surface area.

Once a common unit of measure, the grain is rarely used today, other than in the measuring of propellants and bullets. 1 grain is equal to  64.79891 mg, or 0.064 grams. You may notice weights on ammunition containers, and this will be for the specific bullet used.

Primer

The primer is the friction sensitive means of ignition of the propellant. It is the firing pin of the weapon that contacts the outer casing of the primer, pinches it against an internal anvil, and ignites the very small quantity of primary explosive compound containing barium nitrate and lead styphnate. The resulting flame is then directed through flash holes to ignite the propellant. For the ammunition we use, there are two types of primer used; centre fire and rimfire.

Ammunition fitted with centre fire primers are the most common, found in ammunition of all varieties across the world. In this type, the primer is central to the base of the round, and is what we would recognise as being the portion of the ammunition stuck by the firing pin. A primer hole is required to be manufactured into the base of the cartridge case, into which is pressed the primer cup.

The second type of primer is simpler to manufacture, but not suitable for use in the demanding situations of military ammunition, and this is rimfire ammunition. Almost exclusively reserved these days for .22″ ammunition. With the primer compound contained in the rim of the cartridge case, the propellant is in direct contact with it, eliminating the need for flash holes. The primer is initiated by the firing pin striking anywhere around the edge of the rim, compressing the compound and igniting the propellant.

Projectile

Often referred to as a bullet, the term projectile is technically more accurate as some weapons do not use bullets; such as shotguns or grenade launchers. However, the rifle ammunition we are looking at does use traditional bullets, so we will continue to use the term.

In the cadet force, we use two types of bullet; the solid lead type with the CSBTR, and the metal jacketed type with the full bore rifles. So what are the differences? Muzzle velocity is the main factor in bullet design.

The relatively small and low pressure round of the CSBTR leaves the barrel just above the speed of sound (roughly 330 m/s). We consider this to be low velocity in weapon terms. The low volume of propellant is sufficient to burn at a rate that forces the solid lead round down the barrel to its maximum velocity. As the gas form the propellant expands, it forces the bullet out of the case and into the rifled barrel, but the bullet is slightly too large. Lead, being a very soft metal, changes its shape to accommodate the rifling in the barrel, and to form a gas tight seal preventing any of the expanding propellant gases to escape. You may notice that the rounds are waxy to touch? These are known as outside lubricated bullets, and the lubricant is generally a mixture of vaseline, beeswax and graphite. With jacketed bullets, the metal jacket sufficiently reduces friction to avoid the use of lubricated bullets.

If a solid lead bullet was the be subjected to the increased pressures of a larger bullet case, it would deform to such an extent that it would not be in one piece leaving the barrel. But conversely, if we covered the .22 bullets with a metal jacket, the pressure of the small amount of propellant would not be enough to get it down the barrel. A solid lead bullet has very little penetrating power, in the range once it hits the steel back plate the bullet will deform and most likely break up.

Looking at the basic external anatomy of a high velocity bullet, there are a number of components that they all have in common.

• Body – Often with a lead core, most modern military ammunition also contains a steel core to enhance penetration properties. The outer case or jacket of the bullet is made from soft copper. Technically they are not pure copper jackets, but a 90:10 copper zinc alloy, but the term Full Metal Jacket (FMJ) is used to describe the bullet type.
• Boat Tail – The base of a bullet is profiled to aid aerodynamics and stability. In the case of our high-velocity rifle ammunition, the base profile is known as a boat-tail.
• Ogive – A technical term for the curved profile at the front of a bullet. The radius of the ogive is calculated as being 6 times the diameter of the bullet calibre. The ogive is critical to the aerodynamic properties of the bullet.
• Cannelure – This is the grove around the top of the bullet body used to assist fixing into the cartridge case.

This bullet design is known as a spitzer. A German term for a bullet with an elongated ogive.

The NATO standard 5.56mm bullet is designated as the SS109. It is a full metal jacketed (FMJ) projectile with a steel tip and a lead core.

The 7.62mm bullet is designated SS77/1 and is similar in design to the SS109, with a steel tip penetrator and a lead core. The SS77 design of bullet has a solid lead core. As with most high velocity ammunition, it is also FMJ.

The science behind the flight of a bullet is known as ballistics. While this discipline is outside the scope of this article, it is broken down into 4 main areas:

• Internal ballistics – The science behind what happens inside the weapon. This is the interaction between the propellant and the bullet.
• Intermediate ballistics – Covering the moment the bullet leaves the muzzle and is no longer being acted upon by the propellant or barrel.
• External ballistics – The flight of the bullet through free air.
• Terminal ballistics – The target effect once the bullet arrives at its target or enters a medium that is no longer free air.

Depending how this article is received, I may explore ballistics further. In particular, external ballistics, which of course we apply every time we aim off for wind.

Technical Specifications

The table below is a technical comparison between the weapon systems and their ammunition. There is far more information here than you will ever need to know, but it will help us to draw comparisons between the performance of the various ammunition types.

Terminology

In the table above, there was a lot of terminology you are probably unfamiliar with. As I explain what some of this means, it should also broaden your understanding of the effect altering some of these factors will have.

• Calibre – The internal diameter of the bore of the barrel, which generally equates to the outside diameter of the bullet; however, not always.
• NATO – North Atlantic Treat Organisation. In ammunition terms, it means that member states of NATO can produce ammunition to the same specification.
• Grain – Already mentioned in the propellant section, grains is a unit of measure often used to weigh
• Muzzle Energy – The amount of energy imparted from the burning of the propellant to the bullet as it leaves the muzzle.
• Rifling – In order to impart stabilisation to the bullet, it is spun. This is known as spin stabilisation. The calibre of the bullet will generally dictate the spin required for optimum stabilisation. As a bullet is propelled down the barrel, it is forced into rifling inside the barrel to impart the twist. The high points are know as lands, and the low points are known as grooves. It is rifling that leaves the marks on the bullet after it has been fired.
• Twist – The direction the bullet will spin. Generally this is to the right or clockwise.

Calculating Muzzle Energy

In this section, we can start to use some of the data in the tables above to calculate the forces and energy involved at various stages of the bullets flight. As with all mathematical and physical calculations, we must be certain of the units involved. For the calculations below, I will use SI units – meters, kilograms, seconds and Joules.

The muzzle energy of a bullet is the kinetic energy that it has as it leaves the muzzle of the weapon. Once out of the barrel the propellant no longer assists the bullet and environmental factors (mainly air resistance or drag) start to take over and slow the projectile. This number can be calculated using the standard equation for Kinetic Energy:

Where ME is the kinetic (or muzzle) energy in Joules, m is the mass of the projectile in kilograms (Kg) and v is the muzzle velocity of the projectile, in meters per second (m/s).

Because the muzzle velocity is directly connected to the velocity of the ammunition, this means that the same ammunition through a different weapon with a different barrel length will have an impact on the muzzle energy. Shorter barrelled weapons typically have lower velocities, and therefore a lower muzzle energy.

Unit Conversions

• Grams to kilograms x 0.001
• Kilograms to grams x 1000
• Grains to grams x 0.064
• Grams to grains x 15.432
• Joules to foot-pound x 0.737684
• Foot-pound to Joules x 1.35582

Example (CSBTR, 0.22 LR)

Following through the calculation, we work out that the muzzle energy of the CSBTR is around 178 Joules. Did you follow that through?

Questions

Now it’s your turn. You will need a calculator, a pencil and some paper for your calculations. Using the large specification table above, see if you can calculate the muzzle energy for the Cadet GP and Cadet Target Rifles. You can click on the (i) at the top left of each question for a hint – the answer is not the same as the muzzle energy included in the data table!

ME Summary

What conclusions could we draw when we calculated the muzzle energy of the various weapons?

• The muzzle energy of a 7.62×51 bullet is around twice that of a 5.56×45. But is that really surprising? The bullet weighs over twice as much, and there is both more propellant in the cartridge as well as the rifle has a longer barrel. So not surprising.
• A heavier bullet results in a higher muzzle energy. Again, not necessarily surprising. Applying the same force or energy to a heavier bullet gives that bullet greater kinetic energy. Not only does this mean that it will have a greater target effect, but that the bullet will have the ability to travel a greater distance. It is why competitive target rifle shooters prefer a heavier bullet.
• There is a trade off with firing a heavier bullet; recoil. Newton’s third law of motion tells us “when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.” So, more muzzle energy at the front of the rifle, will mean more recoil energy rearwards into our shoulder. And we know this because we can compare the recoil thump between the CSBTR, Cadet GP and CTR rifles.

Conclusion

Well let’s go back to some of those safety rules we know too well and apply what we now know:

• Never let it lie in the direct rays of the sun as this can cause inaccuracies – Propellant that is too hot, will burn faster. This increased burn rate will cause an increase in pressure, which in turn will alter the velocity of the bullet; causing a hot round to fire differently than a cold round. Not only could it make you miss your target, but this increase in burn and pressure may exceed the pressure the chamber is designed to contain, resulting in a dangerous failure of the weapon.
• Never use a round as a tool – The aerodynamics of a bullet are key to it’s performance. If you have used the tip of a round to unload rounds from a magazine, it will be damaged and therefore not perform as it should.
• Tampering with ammunition is dangerous and is forbidden – With a sensitive explosive compound in the primer, and soft metal cartridge case along with a precisely engineered bullet, any damage to these could result in inaccuracies as well as dangerous conditions. Altering a bullet may also change the terminal ballistics, or the target effect, and this may be illegal.
• Damaged rounds are not to be fired and should be handed into an adult instructor – For all the reasons above, any round that has sustained damage, or been involved in a stoppage shouldn’t be used.

Having looked at the ways of describing ammunition, we should now be able to accurately describe the correct ammunition we use, this being:

• .22″ LR BALL
• 5.56x45mm BALL / BLANK / DRILL
• 7.62x51mm BALL

It is also useful to know the anatomy of a round of ammunition, the cartridge case, the bullet as well as knowing about the primer and propellant.

Finally, we looked at muzzle energy and used the technical data we know to calculate the ME for the two main types of ammunition we use in both the GP and CTR.