Good explanation, but I hope you don't mind if I comment on it to clarify some things? So, wall of words alert, I'll try to keep it simple, I promise:
Dragoon wrote:Caliber is not the only thing that matters when firing solid AP rounds. Actually barrel length is the dominant feature along with the size of the cartridge that holds the charge. A longer barrels translate into a longer acceleration phase and a more stabilized round. Therefore the round reach higher top speed, has improved range and accuracy.
Very good observation about solid projectiles, but the major advantage of bigger rounds is the ability to carry a useful payload, but I'll assume solid rounds to not further complicate things.
A few scientific nitpicks: yes, it's all about speed (velocity), but speed simply comes from being able to put the most energy in a projectile. Because the barrel length is always limited, accelerating the projectile must be done in a very short time. But you are right, the longer the barrel, the longer you have time to accelerate without resorting to very dangerous types of propellants or chamber pressures.
And it's easier to accelerate a light projectile (which usually means small calibre, but I won't go into that), but high acceleration means the projectile needs to be very strong to survive this. So, you want a long barrel, and you'll need a hefty charge of propellant, which you'll need a big casing for, like you said.
About stabilization, you don't need a long barrel for that, contrary to popular opinion. You just need to spin up the projectile enough to avoid it wobbling or tumbling in air for the length of time it takes to reach its target, but very steep rifling will wear out quickly. Today most tank guns are smoothbores with fin-stabilized projectiles, for several reasons.
Improved range: I assume you mean effective range, not maximum range? For effective, real-world range, you are right. For absolute range, fast heavy streamlined projectiles are better than the typical lightweight small calibre round. And a slow, heavy projectile will lose speed at a far lower rate than a small lightweight one, making heavy rounds capable of carrying much more energy at large ranges. This is basically a case of momentum (p=mv) vs the total drag. If two projectiles have the same shape, a projectile that is twice the diameter will be around 7 times heavier. Of course it will have a larger frontal area (higher drag), but the momentum will grow relatively faster than frontal area, making it more effective. Note that momentum and kinetic energy are different, and momentum is often overlooked when determining effectiveness of projectiles.
About accuracy: for real-world purposes, the faster rounds have the advantage because the trajectory is flatter and they cross the distance faster, so they'll need less precise elevation aiming to compensate for the ballistic trajectory. But a ballistic computer with good input data can give slow, heavy projectiles amazing accuracy.
The effective range, which is a combination of energy, ballistics, inherent accuracy of the round, weapon and firing platform, aiming devices and of course the operator(s), is usually higher with the faster projectiles, but these advantages are sometimes offset by other factors. So, you are basically right, but I wanted to clarify some things, since I read this and my teaching sense started tingling:
That speed is so important becomes quite obvious when you use Einstein E=mc², as a raw equation for the kinetic energy aka penetration power of the round. As you see the speed unlike mass is raised by the power of two.
I think you may have confused some theories, Einsteins theory on mass–energy equivalence (E=mc²) is about conversion of energy into mass and vice versa, the kinetic energy is calculated as KE=½mv². Which means that the energy is equal to half the (projectile) mass multiplied by its velocity squared (power of two). So you are correct about the importance of velocity for the kinetic energy, but used the wrong formula. No big problem, but we have high educational standards here, well at least I hope...
Of course to get accurate date you would have to add details for shape and material of the round and armor, air density, temperate etc. but let not get over our heads.
True, it's very complicated, and I only know a few very basic things.
Like all the guys above me already mentioned, the Grand has a short barreled low velocity 75mm barrel, not unlike the early PzIV D-F's had which had only 75cm L24 guns. It was not until the version F2 with 75cm L43, and version G with 75cm l48, they developed real anti-tank fighting capabilities.
Yep. The PzIV initially wasn't even designed to combat other tanks, but for attacking strongpoints and soft targets. The PzIII was suppossed to be the 'main' tank to deal with enemy tanks, but the Germans recognized it would also need a tank with a big, slow projectile that had good HE shells for the other targets. Later on, the only tank capable of being upgraded with an effective 75mm was the PzIV, and ironically the PzIIIN took over the role of the early PzIV models. The Grant basically had both the guns from the early PzIII and PzIV on a single tank.
Of course at the time of the desert campaign, where the Grand was fielded in mass to the British, his lame gun didn't not matter. The Germans and Italians themselves where only fielding either low caliber high velocity, or high caliber short barreled low-velocity guns. There Germans are yet in for the T-34 / KV-1 surprise wake up that caused them to accelerate their tank development and upgrade program.
Well, T-34 and KV-1 were first encountered in June 1941, long before the Grant was introduced (early 1942, with numbers were growing very slowly). And the T-34 was the reason that the German quickly introduced longer 50mm guns on the PzIII (J/1 and up), but this still wasn't enough firepower. The PzIII was at the limit of development, so they continued with the PzIV.
In the desert, the Germans were usually a step ahead in the armament race, which may have convinced them their tanks didn't need much upgrading. And they had started programs (before Barbarossa) to improve firepower, but decided to skip a few steps and speed up in response to the T-34/KV-1, like you say. Only a few of the newer types were sent to Africa, they needed everything on the Eastern Front and the older types could still deal with the British armour. But this was short-sighted as well, because better British/American tanks were just around the corner. Hehe.