Status Report: Guns and ammunition
Author: chickentikka_EU/ Y Liu
I am planning to write a series of articles on common misconceptions regarding tanks. Tell me if you want to see more. (This article is related to my project, so please point out suggestions)
The balance between the power of the main gun (penetration and damage caused) and the effective armor of tanks has been almost in equilibrium for the most part of tank development history. It was after World War II, when the introduction of anti-tank missiles caused the equilibrium to shift towards the offensive. However, obviously armor cannot lag behind the offensive weapons for a long time, so soon composite armor was developed to return the balance. Of course the introduction of ERA and depleted Uranium armor happened to add further shifts in the balance. So I want to resolve some common misconceptions regarding armor and ammunition. (This time round is going to be ammo/gun, maybe armor next time if this article is welcomed).
What do you do to increase penetration? Well, simple, make the caliber bigger and the gun longer! This is true but it depends on the type of ammo. For example, an Indian Army’s T-90S is not going to have the same penetration as Russia’s newest T-90AM although the guns are identical, the shells can make a significant difference. We know that to increase momentum, we have to increase either the mass of the projectile or the velocity, either way we have to increase ammo size or barrel length. The good example is probably the long 8.8cm and the short 8.8cm gun, the longer the barrel, the greater the accuracy and the greater the velocity (in the case of the 8.8cm gun, a longer ammunition is used to pack more punch). However, there is a certain limit to how long the gun can be before it becomes impractical, so engineers after WW2 introduced smooth-bore guns. Smooth-bore is when the barrel no longer has grooves, hence opposite of rifled guns.
|L7 rifled gun.
This means there is less friction, hence the shells will exit the barrel at a greater velocity than rifled guns.
Difficulties with smooth-bore guns are that they lose accuracy as the whole point of rifled guns is to make the shell spin. It works just like throwing a rugby ball or American football, you’ve got to spin it to increase stability and accuracy. The solution to that is to add fins on the shells. Clever isn’t it?
Armour Piercing Fin Stabilized Discarding Sabot, APFSDS rounds and other technology makes modern ammunitions very powerful against tanks. Let’s begin talking about the different calibres!
Classic 105mm guns mounted on M60 or M1 (early variant) had a muzzle velocity of 1501m/s on its kinetic rounds weighing at 5.8kg. The kinetic energy is 6.55 Mega Joules.
Leopard 2’s Rh120 120mm smooth-bore gun has a muzzle velocity of 1650m/s and weighs 7.1kg, kinetic energy is 10 mega Joules. The kinetic energy of the 120mm gun is about 50% more than the 105 gun. The breech pressure of the 120mm gun is 6.3*10^8 Pa which is 6300 times the atmospheric pressure which is about 50% more than the 105mm gun. (Note to calculate penetration we have to convert the values to the standard RHA)
Imagine the kinetic round trying to rip through the thick armour of a modern main battle tank with composite armour. The material in the armour is not all metallic, there are some materials inside it that can really absorb the kinetic energy effectively. After penetration, remember the shell still has to have enough energy to kill the crew etc. Not as easy as you might think it would be.
Be careful tank addicts, penetration values from different nations are done under different conditions so the result may be misleading. Don’t just compare raw data, it can mislead you.
Armour on modern main battle tanks:
Most modern Main Battle tanks have a RHA value of 600-700mm so 120mm rounds currently will require quite ideal situations to penetrate tanks. Western designer’s solutions are generally to increase length of barrel and improve ammo types, but the potential in the 120mm guns can only go so far (so not room for improvement anymore).
Most people know that Western countries (NATO) tend to use 120mm guns and Soviet (Russian/Chinese) guns are 125mm. Historically, Americans developed a 90mm, the Soviets then designed the 100mm, then NATO used 105mm which led to the Soviets to design a 115mm and so on until the recent 125mm. Almost every Soviet design wants to remain 5mm or 10mm greater than that of the NATO guns of the same period.
You would think that power is greater with bigger guns because as the dimensions increase, more gunpowder can be filled. Not always the case, let me tell you why.
- Power of shell depends on the amount of gunpowder
- The type of gunpowder
- Shape of projectile
- Size (mass) of projectile
- Breech pressure etc.
Here I would like to use an interview with the father of the Type 99 MBT.
This tank designer was in his 90s when he finished the Type 99 project (he only had one arm due to the Korean War). He died recently and received many awards for his outstanding courage to take up a new project as head designer at the age of 80. (Interview is here, not in English though but is quite useful information)
So during the interview, he was asked why did you choose 125mm gun and not the 120mm when some people argued that 120mm gun was better (because Western designs are supposed to be better)? He replied: 120mm rounds had a capacity of 9.8 liters and 125mm rounds had a capacity of 13.4 liters. So Russians with poorer gun powder can still achieve power equivalent to the 120mm guns by simply filling more gun powder. After improving quality of the steel and production quality, the Type 99’s gun had better power than its opponents. (Note: other countries also improve so the comparison was based on existing operational guns, Type 99’s 125mm comparison was done with 125mm from T-72)
During the designing of M1A1 and Type 90 (Japanese), America and Japan both wanted to produce their own 120mm however, it turned out that it was so difficult that they instead just bought the production license from Germany. (Really says something about German engineering).
Let’s compare the 125mm (Russian) gun’s kinetic energy which is 9.6 Mega Joules, hang on! Wait, why has the 125mm got less kinetic energy than the leopard’s 120mm’s 10mega Joules?
Well, it just tells you that can’t simply compare the calibre. I want to emphasize that the gun on the Armada is supposedly better than the 125mm on the T-90 so you take that into perspective as well. Just like the fact that the Norinco (Chinese) 125mm on the Type 99 is superior to the T-90’s gun although the same caliber does not mean same power.
Now, let’s talk about 140mm gun. 20 or 30 years ago, Swiss and German engineers began designing the 140mm guns which was fitted on leopard 2 for firing tests. It proved that 140mm was viable on main battle tanks so British Royal Ordnance Nottingham also produced a 140mm for testing. But due to relaxation since there will be no urgent need to fit 140mm gun for a new major ground based war, it is not going to be implemented soon.
According to declassified documents, modified 120mm smooth-bore guns have a maximum penetration of 700-750mm RHA penetration while 140mm has 900-930mm RHA so the penetration value increased by 30% from the 10 mega Joules to 15-16 Mega Joules (50% increase).
Why don’t we fit the 140mm?
- Gun barrel made more compact with stronger and thicker barrels to withstand the increased pressure (6400Pa (120mm) to 8000Pa (140mm)) .
- Solve recoil issues, the recoil of 120mm firing APFSDS has a force of equivalent 40-50 tons. 140mm has over 60 tons.
- Reduce the burning caused by friction in the barrel. This is required to increase the life span of the gun. No point having a gun that requires replacement every few hundred rounds
- Increase reliability of auto-loaders, currently firing around 20 shells, there will be at least one problem. Although when problems occur, it can be switched to manually reloading but 140mm is way heavier to handle.
- The shell (ammo) has to be completely redesigned to adjust to the changes. So, increasing dimensions results in less shells being carried.
- Many features of the tank has to be redesigned to accommodate the new gun. Turret side etc.
The data from the 140mm gun from the leopard 2 shows the barrel length is 47 times the barrel diameter. Breech pressure being 8000Pa and material of the shell is Tungsten Alloy. (W-Ni-Fe、W-Ni-Cu、W-Ni-Cu-Fe)
It seems like 140mm guns are ready but placing it into service in what kind of scale remains a question of international situations. I just want to round off this by mentioning a type of ammo using depleted uranium. Depleted uranium is favored by the gunner for penetration because it is self-sharpening and flammable.
Depleted uranium is harmful and it is used in both ammunition and armor. Many countries have the technology to incorporate it into their tanks but choose not to, a good example is the Type 99 reportedly having such modifications but not mass produced because the nation is not in a war and would harm operators through radiation. If you ask me if depleted uranium should be allowed, I just say that it depends on the results gathered if the radiation is life threateningly dangerous or not.
Hopefully you have enjoyed this article. I will talk about other types of defenses if you want to see more on this topic (probably talking about ERA, active and passive defense systems including laser weapons on tanks or special guns designed to push people out of buildings).
Written by chickentikka_EU/ Y Liu and edited (checked by) Farmeh_EU