Learning about modern main battle tanks, some of them have 120mm main guns that have a smooth bore muzzle as opposed to rifling. Historically, muskets and other muzzle loaded rifles weren’t considered accurate at anything resembling long or even moderate range. Rifling of the barrels dramatically increased accuracy. Have main battle tanks ever used rifled bores, and if not, how can the smooth bores be accurate enough to effectively engage targets at ranges over 3,000m?
In: Engineering
Rifled bore make the projectile spin, which make it more stable in flight and increase the accuracy. But making the projectile spin isn’t the only way to stabilize a projectile. Tanks used rifled gun for a long time, but some specific projectile used by modern tank are better without rifling.
One of them is the HEAT round is an explosive that shape a jet of molten metal to pierce the tank. HEAT round are more stable in a rifled barrel, but the spinning decrease their effectiveness on target. So in that particular case you could make a case for both rifled or smoothbore gun.
But the main reason why modern tank use smoothbore today is because of APFSDS. Those are Armor-Piercing, fin-stabilized, discarding Sabot. Those are like arrow, long but narrow with allow them to concentrate their force into a small area which make penetrating easier. You see in the name that it’s fin-stabilized, so it doesn’t need to spin to stabilize itself, in fact making that round spin would create air resistance on the fin which wouldn’t be good.
The M1 Abrams for exemple used to have a 105mm rifled gun using APDS (Armour Piercing Discarding Sabot). The problem is that APDS had a limit on how narrow you can make the round before it become instable even if you spin it. It’s about the ratio of diameter vs lenght, once the projectile is about 6-7 times longer than it’s diameter, spinning the projectile just don’t do it, so fin were used and for that you need a smoothbore gun.
A computer takes all the data and generates a ballistic solution instantly. There’s a traditional sight too but it’s a bit more complicated than just looking through a scope. Without the rifling the projectile drifts, but the drift is always the same. So smoothbore just needs some extra math.
Rifling has been used in modern tanks. The Abrams originally had a 105mm rifled main gun. Then we switched to the German made 120mm smooth bore.
There are a lot of advantages to smooth bore, and all the negatives can be negated.
The precision of those smoothbore cannons is _significantly_ better than any musket. They’re also computer-controlled to compensate the vehicle movement (be it ocean wavesor land inconsistencies) and aim.
Some tanks use sabot rounds, too, which interact differently with rifled barrels.
Muskets in general fire a round ball. The ball have bad aerodynamics when if flight and any unsymmetrical part will have a effect on one direction. The did not fit the barrel perfectly because muskets was in general muzzle loaded so you need to be be able to push it down it to load it, this can result in some bouncing in the barrel that reduce accuracy.
Rifled increased accuracy because the spinning make it stable like a gyroscope and any unsymmetrical part will not longer push in one direction but get canceled out because of the rotation.
Tank guns are breech loaded so the shell fits perfectly and is of hard precision manufactured stuff not lead that can get deformed when fired . What you fire out of them is not a round ball but [HEAT shell](https://en.wikipedia.org/wiki/High-explosive_anti-tank_warhead#/media/File:125mm_3BK29_HEAT.JPG), [Armour-piercing fin-stabilized discarding sabot (APFSDS)](https://www.militaryimages.net/media/apfsds.33143/full) and some more types that if you look at them all have fins that is used to stabilize there path.
So they way that they are stabile in the air is just like a arrow.
You can see the difference if you drop a arrow or a ball from some height and the effect of wind on each.
Tanks used to have rifled cannon in the past. The first smooth bore tank guns was introduced in the 1960 because the long APFSDS projectile, HEAT shells and anti tank missiles fired from the cannon work a lot better with a smooth barrel. The Soviet T-64B main battle tank was the first tank that used that.
Today most tank design uses smooth bore guns because APFSDS and HEAT is the best ammunition to defeat other tanks. The fins on the projectile will keep them stable in flight. Fins that deploy or is a part of the projectile make the ammunition more complex so it is nothing you would like to do on small caliber guns. You add the complexity when it is needed like for HEAT even on man portable launchers. There are experiments with [https://en.wikipedia.org/wiki/Needlegun](https://en.wikipedia.org/wiki/Needlegun)
There are British Challenger 2 because they what to be able to used High-explosive squash head (HESH) that squashes explosible on the target and detonate. It is good against solid amour and bunkers. You can fire APFSDS and HEAT from them by having rotating drive bands, think of a ball bearing, so they do not rotate when fired from rifle gun.
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