koti wrote:
Yes. What I wanted to say is that the modified rounds be issued for C.I and QC roles. My Idea is to replace AK's with Insas that are used in these roles just by using improvised ammo.(No comment on ruggedness though)
That is if the new rounds would be able to provide as much stopping power as standard 7.62x39.
Easier said than done. Let me explain the issues involved here (apologies in advance for any boring stuff you may find).
First, we study the equation for kinetic energy from middle school physics:
Kinetic energy = 1/2 * m * v * v
where m = mass of object and v = velocity of object.
Clearly, to increase the kinetic energy, we must increase mass, increase velocity or increase both. Let us study the issues of each of these:
1. Increasing Mass of bullet
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Modern bullets are made of a lead core with a thin jacket of steel, cupronickel or copper alloy. The mass is mostly due to the lead content. Lead is used because it is a dense material that is easily shaped. To increase the mass, you could either:
a. Use a denser material than lead, or
b. Increase the size of the bullet (length and shape), or
c. Do both
Now if you look at a periodic table, it is pretty hard to find another element that is available in large enough quantities to be cheap, but still have high density. Most of the elements that are located above lead in the periodic table are either rare, volatile, gaseous, radioactive, expensive to refine, or a combination of all these properties. You may be able to replace lead with depleted uranium or thorium, but these are much more expensive to produce. That's why people use depleted uranium for anti-tank rounds only, because the cost involved is prohibitive for mass produced ammunition.
If the designers choose to increase the size of the bullet instead, they have to redesign the chamber and firing mechanism so that the cartridge fits tightly in it. They will also need to change the magazine to accommodate the bigger cartridge. Lastly, if they choose to increase the size by increasing the diameter of the bullet, they'll need to change the barrel as well. This means that they will need to change quite a few significant parts of the rifle system, or introduce a new rifle model to use the bigger cartridge. Another alternative would be to use a thinner outer jacket of the bullet and add more lead in the core, which will increase the weight without increasing the size, but you can only make the outer jacket so thin without compromising the bullet's shape when fired. This is why the difference between different variants of NATO 5.56 bullets is only about 0.1 gm or so. They can't make it much heavier than that, without altering the size past the point that existing rifles won't be able to fire it. Changing the size of the bullet also affects its ballistics, so the barrel may need more rifling twist to ensure that the bullet stays stable in the air during flight. Thus we see that increasing the size of the bullet significantly will necessitate introducing a new rifle as well.
Note that if they increase the bullet mass alone, the kinetic energy won't change because the thrust acting on the bullet is caused by the burning propellant (usually some form of cordite) in the cartridge. If you use the same amount of propellant and a heavier bullet, the heavier bullet will simply travel slower, because of law of conservation of energy. Therefore when you increase the mass of the bullet, you must also fiddle with the propellant to propel it to greater speeds, which brings me to my second point of discussion
2. Increasing the velocity of the bullet
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Increasing the velocity of the bullet can be done by:
a. Using more propellant (cordite) in the cartridge
b. Change the chemical composition of the propellant to a more effective one that produces more energy.
If the designer adds more propellant to the cartridge, this will change the size of the cartridge, which will require them to alter the size of the chamber, magazine, extractor etc. which means that they will need to manufacture a new rifle, as existing rifles won't be able to use the cartridge.
If they change the chemical composition of the propellant, this may not change the size of the cartridge, but it may have a more corrosive effect on the barrel (this actually happened to M16s early on in their history -- one bullet manufacturer used a different type of propellant and caused corrosion in their barrels that couldn't be cleared because no cleaning kits were issued. The lower powered propellant that the rifle manufacturer tested with didn't react with the barrel.)
Also, the problem with both these approaches is that the extra energy delivered to the bullet means that the barrel and chamber will experience higher pressures than what they've been designed for. This means that there is a risk of the barrel or chamber exploding due to the increased pressures. For example, nitroglycerine or C4 have more explosive power than cordite, but no one uses them in cartridges because they will cause the barrel and firing mechanism to fly apart and send shrapnel everywhere. To handle increased pressures, the designer will need to make a thicker barrel and stronger firing mechanism, which means a new rifle and also a heavier one.
Also note that the barrel length will need to be changed, because if the barrel length is not long enough, some of the powder will burn outside the barrel and cause tremendous vibration and flash, making the rifle hard to control. This was the problem faced by the INSAS carbine -- it couldn't use the same cartridge as the INSAS rifle because of this issue and the designers solved it by making it use a smaller cartridge that uses less powder.
So you can see that to increase the kinetic energy of the bullet significantly, the designers will likely have to go with a new rifle as well. There are quite a few people who think that NATO 5.56 doesn't wound enough to incapacitate and suggest a bigger rifle using a 6mm or 6.8mm cartridge for this reason.