Main Guns on MBT’s
There are two types of main guns used on tanks, rifled and smoothbore. Both have advantages and disadvantages.
Rifled – cannons have a spiralled pattern of grooves inside the length of the cannon. These grooves imparts a spin to the fired round which stabilizes its flight and prevents it from “dropping off” (falling to the ground as gravity takes over) giving the round greater accuracy and increased range. It is also this pattern that is used to arm HESH rounds, a popular round with the British Army.
The larger 120mm rifled cannons use a bag charge system. The round is first loaded into the breach and then a satchel or Combustible Case Charge filled with the propellant is then loaded. Using a two part bag charge system prevents the loader having to man-handle larger rounds as used by Smoothbore cannons, is able to load faster and reduces the level of fatigue of the loader.
Smoothbore – The energy released from the combustion of the rounds charge builds up behind the round as it travels down the main gun. Some of the energy escapes through the grooving of the rifling. Energy doesn’t escape with a smoothbore, which requires a slightly higher level of muzzle velocity to try to stop the round from dropping off due to the lack of the spin from rifiling. Smoothbores use one part rounds and store these in one large box in the rear of the turret. The imparted spin from rifling also breaks up the copper jet released from a tank fired shape charged weapon, which is called HEAT, diminishing its effectiveness. The use of HEAT was one of, if not the principal reason many countries decided to use smoothbores in the last 30yrs or so.
Calibre
A tanks Main Gun is measured in two ways:
Barrel Bore – is the width of the muzzle. The bigger the muzzle, the bigger the round, the more damage it causes.
Barrel Length – had been an area in design and development within Europe (outside of the UK who had already done this) during the 90’s. By increasing length, the round has further to travel down the barrel, which means the energy from the charge has longer to build up, pushing the round hard out of the muzzle, increasing its velocity. This is called “Muzzle Velocity” and is measured in the number of meters the round travels in a second, AKA “m/s”. By increasing the m/v you increase the m/s. The higher the m/s, the round takes longer to fall off and increases the range and accuracy as well as the punch to get through the enemies armour.
Machine Gun Cal. – are measured either in inchs or mm and can be converted between the two. A 30cal. is the equivalent to 7.62mm and a 50cal. is the equivalent to 12.5mm.
Other effective parts of Main Guns
Thermal sleeve – The main gun on an AFV tend to be long and consequently there is a tendency for the barrels to distort when they are subjected to differential heating conditions such as the heat of the sun on one side of the barrel and a cold wind on the other side. Accurate long range shooting depends upon the barrel being perfectly straight and in order to insulate the barrel from the effects of the environment, it has become standard practice to provide one or more thermal sleeves for the barrel. Such sleeves commonly comprise blankets of asbestos and/or glass fibre wrapped around the barrel.
Breech – These type of loaded weapons have been around since 1770, The major advantage is that it is a lot easier to load a round from the rear of the weapon and not have to ram the projectile from the muzzle through tight tough rifling’s often a timely and laborious action this speeds up loading and in turn the engagement sequence. Breeches on tanks are used to seal of the back of the weapon simply acting as a cork.
They often comprise of many complex mechanical parts, in the L30’s case it houses and delivers the electrical charge needed for firing. In other tanks such as the Abrams and Leopard2 the breech houses the firing pin assembly and hammer used to strike the rear of the one piece round. The breech on a modern tank gun has to sustain massive amounts of shock and heat caused by firing. They are made from high density metals and are very heavy. The breech blocks are held and locked in place with a powerful torsion bar spring, this enables the breech to be closed quickly during the loading process.
Auto-Loader – is a mechanical machine used as a replacement of the human loader AKA operator. It is embraced by some countries and shunned by others as it has a number of pro’s & con’s. developed at the end of WW2, the system extracts a shell and propellant charge from a magazine, loads it into the chamber of the gun, and closes the breech.
The system takes up less space than the human loader in the turret, thus saving space and allowing the turret height to be reduced as the operator normally has to stand while the commander and gunner sit. The reduction in height means a lower profile making the vehicle a harder target to hit and can reduce the overall weight by up to 25tons.
An auto-loader is not a reliable system. If the autoloader fails, manual loading becomes very difficult because the autoloader takes up the space were the operator would have been. The speed of which an auto loader can load is normally matched by a human loader, thou there are claims an operator can load faster.
The loss of the operator has a negative effect on the crew. He can be used as a lookout, emergency backup driver/gunner, mechanic and sentry.
Most common main guns used on Main Battle Tanks
L30 – is the current cannon fitted on the Challenger 2. Developed and manufactured by the former RO Defence, it is now manufactured by BAE Systems Land Systems. It is a 120mm rifled cannon made of steel and manufactured using a process called electro flux re-melting. It has a chromium alloy lining to reduce the wearing on the spiralled pattern of grooves associated with rifled cannons. It is a cal Length 55.
The L30 fires APFSDS, HESH, DS/T Prac & SH/Prac (practise rounds) and WP Smoke rounds.
L11A5 – was developed and manufactured by the former British RO Defence. It was the first 120mm rifled cannon and was used on the Chieftain and Challenger I MBT’s.
L7 – was a 105mm rifled cannon. It was developed by the former British RO Defence and fitted to the British Centurion MBT. It was recognised as a highly effective cannon and adopted by practically every NATO tank. It was equipped on the – Brazilian EE-T1, ROKA K1, German Leopard 1, US M47, M48, M60 & M1 Abrams, Israeli Merkava MkI & II (AKA M68), Magach, Sho’t, Italian OF-40, South African Olifant, Swiss Pz 61 & Pz 68, Egyptian Ramses II, Swedish STRV 103 S (AKA L/62), Israeli Tiran-4&5, German TAM (early production), Japanese Type 74 and Indian Vijayanta and is still being pressed into service with modern AFV’s, notably the new US Stryker MGS.
It could/can fire HE, HESH, HEAT, APFSDS and Smoke rounds.
L44 – is a highly successful 120mm, 44 cal (length) smoothbore cannon. Designed and manufactured by the German Company, Rheinmetall, for the Leopard 2 up to and including the A5 variant. It is built under licence in Egypt for the M1 Abrams, in Israel for the Merkava III & IV (AKA MG251 & MG253 modified), Japan for the Type 90, South Korea for the K1 A1 (AKA KM256) and in the US for the M1 Abrams (AKA M256).
It can fire APFSDS, HEAT, MPAT, Canister and HE-FS.
L55 – is the successor to the L44. it to is a 120mm, 55 cal (length) smoothbore cannon, designed and manufactured by the German Company, Rheinmetall. With its extra length it provides a higher muzzle velocity. It is currently used on the Leopard 2 A6 and the newly developed South Korean K2 Black Panther. It did complete trials on the British Challenger II, but there are no plans in the near future to equip it. It can fire the same rounds as the L44.
D-10 – series was the primary Russian 100mm rifled cannon for its medium tanks, the T-54 & T-55 series. It was up-graded a number of times (D-10S, D-10T, D-10TG & D10T2S) and equipped on Russian tanks up to 1979.
It could/can fire HE, HVAPDS, HEAT, APFSDS and 9M117 Bastion anti-tank missiles.
2A46M – is a smoothbore 125mm cannon manufactured in Russia and used on the T-72 & earlier models of the T-80. It is capable (with the right ammunition) of taking out NATO tanks and is as powerful as the L44.
CN120-26 – is a 120mm smoothbore, 52 cal. in length cannon, providing higher muzzle velocity then the popular L44. It was developed and manufactured by the former French GIAT Company. It is equipped on the French and United Arab Emirates Leclerc MBT. It can fire APFSDS, HEAT and a reported 18 other types of rounds. It is compatible with other NATO manufactured identical rounds (i.e. It can fire APFSDS manufactured in US) but uses indigenous manufactured rounds.
Ammunition Types …. common forms
Muzzle velocity – is the term used for the speed at which a round (ammunition) leaves the main gun. The muzzle is the external end of a main gun and as a round exits the muzzle it begins a gradual loss of velocity (speed). The higher the muzzle velocity, the further the round will travel and the more force it will have behind it to push the round through the armour of another tank. It is normally measured by how many meters (m) or feet (ft) per second the round will travel at the point it leaves the muzzle. For example – an average kinetic energy penetrator round, has a muzzle velocity of 1500 m/sec. Armies all around the world are always trying to increase the muzzle velocity of their cannons. This is done through the type of propellant and how much of it they use, the type of ammunition and the materials it is made of as well as increasing the length of the cannon.
Kinetic Energy penetrator AKA “KE weapon” – is a round that relies on kinetic energy to push it through enemy armour, rather than chemical energy from an explosive. Kinetic energy is the energy of motion and generated by the mass and speed of the round. KE increases when the speed of the round increases, which is achieved through a high muzzle velocity. The bigger the surface of the round that makes contact with the enemy armour, the more energy is lost. So by reducing the surface of the round that makes contact with the enemy armour to a point or tip, the kinetic energy is focused and increased, giving it the shear brut force to push through enemy armour.
Shaped Charge – weapons, are used in tanks and Anti-Tank Missiles (AKA “ATM”). The main shell houses the explosive and a hollow funnel shaped cavity (narrowest end faces the bottom of the round housing the detonator and surrounded by the explosive and the widest end at the top) lined with a metal, most commonly copper, but different metal materials are used depending on the material of the target. As the round hits the enemy surface, the force of the explosive blows the funnel shaped copper liner inside out into a forward moving collapsed jet of heavily heated copper at a supersonic speed, which then burns and pierces the armour surface, striking explosive materials like ammo or hydraulic fluid.
Ammunition Types …. the basics
Armour Piercing Fin-Stabilized Discarding Sabot AKA “APFSDS” –
The APFSDS is a KE weapon and a modern day version of the arrow. Generally they are rods, 2-3 cm’s in diameter and 50-60 cm’s in length. It is made out of dense material, Depleted Uranium, Tungsten or Staballoy so that when the tip impacts armour it doesn’t “mushroom” & holds it pointed shape, retaining its KE. It’s held in place by a sabot, which then comes away as it exits the cannon and the fins provide the round stability. It’s a non-explosive round and relies on hitting the enemy ammo or fuel tank so it explodes or maims the crew. Generally its muzzle velocity is 1500 m/sec when fired from a calibre Length 44 main gun and 1750+ m/sec from a calibre Length 55 main gun.
High Explosive Anti Tank AKA “HEAT” –
High Explosive Anti Tank rounds are explosive shaped charges used and fired by smoothbore cannons, as they are less effective if they are spinning, as this breaks up the metal jet of the inverted liner on impact. In order to penetrate new thicker/deeper armour, the length of the metal jet has to be increased. This is achieved by making the width of the round larger, increasing its calibre. This then means the calibre of the tank cannon has to keep on being increased, so it is less effective as a tank round due to the restrictions of the calibre of the tank cannons. Many NATO countries use HEAT as an alternative to HESH to defeat AFV. More modern HEAT rounds have a multifunctional fuzing system which allows the round to explode and fragment in mid-air.
High Explosive Squash Head AKA “HESH” –
HESH was invented by the British aeronautical engineer Sir Charles Dennistoun Burney as a concrete bunker buster for AVRE mortars during WW2. During this time it was found to be effective against AFV’s. It is a thin metal case packed with plastic explosives. It only works when fired from a rifled cannon, as the grooves arm the delayed fuse. On contact with the enemy surface, the explosive spreads across it and the fuse ignites it, generating a large enough shockwave to destroy buildings. On AFV’s, the shockwave travels through the armour, and blows off a disk the size of a saucer from the inside surface of the armour, which then fly’s around inside the tank, maiming the crew or striking explosive materials like ammo or hydraulic fluid. Thou more modern HEAT rounds can be used in the anti-personal role, HESH proves to be more effective in this role as well as demolition of concrete strength structures and light skin vehicles.