Cartridge design

A cartridge is a unit or round of ammunition consisting of a projectile, propellant to thrust the projectile from the gun, a primer to ignite the propellant and a cartridge case to hold it all together. For as long as it has been used, the cartridge has been the heart of all automatic weapons. It is almost invariably designed first and the gun configured around it. This particularly applies to gas- or recoil-operated automatic and semi-automatic weapons because their functioning depends upon the characteristics of the ammunition; not just the size and shape but also the gas pressure and recoil generated. These factors are less significant in externally powered weapons such as chain guns and most rotary cannon, but these form only a minority of the guns in service.

While it is not uncommon for different guns to be designed around the same cartridge, it is therefore rare for a service cannon or HMG (heavy machine gun) to be adapted to fire a new cartridge. The few exceptions are generally concerned with an alteration to the neck diameter of the cartridge case in order to take a projectile with a different calibre. The best-known example of this is probably the German MG 151 aircraft cannon, which commenced life in the 1930s in 15mm calibre but was increased to 20mm during the Second World War.

Cartridges are designed to achieve particular effects. The official requirement might specify the ability to penetrate a given thickness of armour at a particular range, a maximum time of flight to a given range, or the effectiveness of incendiary or high-explosive projectiles. There will also be a range of other criteria including acceptable levels of accuracy, consistency, reliability and safety, which will need to be sustained over a wide range of climatic conditions and a long period of time. These only

PROJECTILE

driving band neck

CARTRIDGE CASE

CARTRIDGE CASE

Heavy Ball Ammo Can

neck crimp (segmented)

shoulder case body belt

Draw Extractor Gun

head shoulder case body belt extractor groove head crimp (segmented)

extractor groove

Elements of a ecmnon eartridge (drawing courtesy of J-F Legendre)

T II IÏ C A U T R I » ii Ml partly apply to blank cartridges and not at all to projectiles can be quite colourful.

drill or dummy rounds, but these types will not be considered here.

Ball ammunition is the simplest and is named after the round lead balls which were the standard

For use in automatic weapons (except in the case small-arms projectiles until the nineteenth century, of externally powered guns), it almost goes without The name is still applied to standard rifle ammuni-

saying that the ammunition must be able to operate tion, in which the bullet consists of a jacket (origi-

the gun mechanism reliably. This might not be a nally copper, now a variety of alloys) normally simple matter given that the projectile weights and enclosing a lead core. Ball projectiles are not now propellant powders can vary considerably in differ- common in heavy-weapon ammunition as they have ent loadings of any particular cartridge, and this limited effect on the target in comparison with can alter the recoil and pressure characteristics more specialised projectiles. Where they do occur, accordingly.

The projectile

Everything else - the rest of the cartridge and the gun itself - is concerned with ensuring that the projectile hits the target at the desired velocity. The design of the projectile is therefore the most crucial aspect of ammunition design.

Projectiles are available in a wide variety of types, even ignoring those intended for practice or drill purposes. Service ammunition can be classified into four broad categories: ball, incendiary (I), high-explosive (HE) and armour-piercing ( AP), any of which may also be equipped with tracers (T) so that the gunner can observe the accuracy of his shooting. Other common designations are SAP (semi-armour-piercing), TP (target practice), SD (self-destruct), APDS (armour-piercing discarding-sabot)and APFSDS (armour-piercing fin-stabilised discarding-sabot). The terms HV (high or hyper velocity) and SV (super velocity) are sometimes used to designate lightweight projectiles (usually AP). Some manufacturers use their own designations for proprietary types of projectiles.

Cannon projectiles are usually painted according to their type for rapid identification purposes (in HMG projectiles it is normally just the tip that is painted). Colour schemes have varied between nations and military blocs and within such groupings over time, so this is not the place to attempt a complete listing. However, AP projectiles are nowadays commonly painted black and practice ones blue. Reds and yellows frequently indicate chemical contents, either HE, incendiary or tracers. Combined projectiles often have bands of colour to indicate their particular mix of characteristics, so they usually have a predominantly steel core. Most heavy weapon projectiles now in service have armour-piercing, incendiary and/or high explosive

The projectile is what the weapon is all about. capabilities.

The method of projectile construction varies

30x170 Cannon
Fired 6pdr A P projectile showing driving band engraved by the rifling
Sabot Plastic SleevesChemically Engraved Armour
Experimental 40mm APDS projectile

great improvement in the performance of APCR at longer ranges, in terms of both reducing the time of flight to increase hit probability and increasing the impact velocity (and therefore armour penetration), without the practical disadvantages of taper bores. It has accordingly seen widespread post-war use in automatic weapons; in smaller calibres the sleeve is nowadays usually plastic. It is not generally used in aircraft weapons because of the potential damage from bits of discarded sabot hitting the aircraft or being sucked into the engines. wSabot diverters" have been designed to try to circumvent this problem, with some success, but they are bulky and heavy.

The most sophisticated type of AP shot is the APFSDS. This was developed as a result of the observation that a long, thin projectile has advantages for AP use, partly because it has less air resistance and therefore does not slow down as much on its way to the target, but also because it can punch through armour more easily. The problem is that there is a limit on the length of projectile which can be stabilised by being spun by barrel rifling: it can be no longer than about five or six times the calibre (an L/D or length/diameter ratio of 5:1 or 6:1). Long, narrow shot therefore have to

Havi Mashin Gun

A PDS components: plastic sabot, tungsten carbide penetrator with aluminium ball is t ic • cap, base cup

Beretta Penetrator20x139 Round

Armour-piercing technology (from left to right): APDS for 20 X 139 with plastic sabot removed, APCR for 20 X 128 with alloy nose-cone and tungsten core removed, APDS for 30 X 170 (Rarden) with sharply-pointed be stabilised by fins and have sometimes been tungsten core

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