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
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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