How does a rifled barrel of a weapon makes a weapon much more accurate?
In: Engineering
To add to the spin part, watch someone throw a football without spin. The ball will wobble in mid air unpredictably.
It’s the same principle with a bullet, except the higher velocity results in loss of accuracy.
Spin is achieved by fine grooves in the barrel, the longer the barrel the more time is has to spin up.
It’s called the gyroscope effect and it’s the same reason why peddling faster makes your bike more stable. The physics of it is rather complex but the simplest version is.
When something spins at a high rate of speed, the pivot point it is spinning around will stay in a fixed orientation. Meaning that a spinning bullet flies straighter and farther without tumbling.
If you want to see more about this affect i recommend this video. https://youtu.be/ty9QSiVC2g0
It imparts a spin on the bullet.
This gives them a more predictable and flight path (predictable as in if you fire repeated rounds they should all hit more or less the same spot on the target if they’re being shot out of a high quality barrel), resulting in higher precision.
Accuracy is essentially the ability to hit what you’re aiming at, so a predictable bullet flight path allows for sighting in of the gun. If you fired 10 rounds and got hits that were each 3-4″ apart from one another on a target 10′ away this would be pretty hard to do. If all the shots hit within a 1″ group it’s much easier.
Rifled weapons are not necessarily more accurate. It is more accurate for the simple cheap bullet but not compared to more complex alternatives.
Most tanks today have smooth bored barrels and not accuracy problems. The one that still used rifled barrels is to be able to use [HESH](https://en.wikipedia.org/wiki/High-explosive_squash_head) rounds or just to keep compatibility with the ammunition of older tank design with the same caliber. If I man not mistake it is the UK and India that still use rifled barrels on new tanks.
The move to smoothbore is not because of increased currency but that long thin [sabot](https://en.wikipedia.org/wiki/Armour-piercing_fin-stabilized_discarding_sabot) and [HEAT rounds](https://en.wikipedia.org/wiki/High-explosive_anti-tank_warhead) work better.
Both smooth bore and rifled tank guns have the same accuracy it is all about the ammunition.
Mortar has smoothbore barrels too. This is primarily because the are muzzle-loaded and you can have thinner walls and more explosive. The fins on the back provide accuracy and you can in a simple way add propellant rings around the narrow tail to control the range.
For a projectile, you like it to point in the same direction all the time so you can spin it that result in a gyroscopic effect so it is hard to turn or you can have fins at that end just like an arrow. In-tank ammunition and mortar shells the projectile has fins on the end just like an arrow and that solves the point in the correct direction problem.
Another advantage of spinning is if the projectile is not perfectly symmetrical there will be uneven air resistance. The projectile will move in the direction of less air resistance. So a nonspinning projectile will diverge in one direction. The direction will if you spin change so on average there is no net moment and it will follow a corkscrew path to the target.
For small-caliber ammunition, you make huge amount where each cost very little to begin with. So any extra work to make it symmetrical or have fins increase cost a lot. So the simple and cheaper option is to spin the bullet.
For a large caliber shell, the cost of manufacturing is already many times higher so making it symmetrical and adding fins do not add a significant amount to the cost. So when long sabots and HEAT round works better you make high accuracy smooth bore weapons. I suspect that you also higher accuracy in the diameter of the projectile so it does not bounce side to side in the barrel.
Rifling was developed back when a bullet was just a molded piece of soft lead. Most weapons were muscle loaded and are able to push down the bullet especially with black powder fouling it had a bit smaller diameter than the barrel. Rifles were added on standard military [Minié ball](https://en.wikipedia.org/wiki/Mini%C3%A9_ball) that expanded when fired so it was fast to load as a smoothbore gun. Specialist riflemen existed primarily for harassment because of their longer range, but the long reload time it was not standard weapons. Some hunters also use them befoe because loading speed is not relevant as it is in combat.
There has been experiment with [flechette guns](https://en.wikipedia.org/wiki/Needlegun). So smooth bore small caliber guns. The advantage is higher muzzle velocity, less drag, and longer range. None have been successful, It is had to make it work at that caliber especially in a cost-efficient way. The did not provide enough advantage to start using them. Making them as accurate is not good enough if they cost a lot more the have to be better.
So you can today make smooth bore as accurate as rifled barrels but the higher cost of ammunition makes it a worse option except for tanks and mortars where you can add ammunition that works better if it does not need to spin.
Rifling spins a bullet, which means it doesn’t wobble. It’s the same thing that causes a spinning top to stay upright, that causes a spinning bullet to stay pointing forwards. By staying forwards and not tumbling, the trajectory of a bullet is much more consistent.
The rifled grooves in the barrel are arranged so that they twist in one direction.
When the bullet travels along the grooves, it starts to spin.
A spinning bullet is less likely to tumble in different directions as it flies.
This is exactly the same as a spinning top. When it stops spinning, it tumbles over.
Set a top on its point on a flat surface and see how long it stays there.
Now spin it and watch how long it stays upright.
Hopefully it stayed upright much longer when spinning than when set on it’s point.
Or if you have a fidget spinner spin it and try moving your arm while its spinning. Notice that it’s harder to move while spinning than when it stops?
That’s because changing the orientation of a spinning object requires energy.
A bullet is moving through a rifled barrel is forced to turn, and once it leaves it continues turning. The bullet moved through the barrel quickly, so quickly it spins at a very high rate (much faster than a top–rifle bullets are often spinning at hundreds of thousands of RPM). So it takes much more energy to change the bullet’s orientation which means all the things that change between shots (like small changes in wind) have little energy compared with the energy required to make the spinning bullet reorient, so it’s more likely to follow a consistent path between the rifle and target.
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