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.
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