Rifling in the barrel is actually grooves cut into the barrel by the manufacturer to cause the bullet to spin as it leaves the barrel. Before rifling the bullets would tend to tumble when they left the barrel causing them to have shorter range and be less accurate.
There are spiral grooves engraved on the inside of a rilfe or pistol barrel. When a bullet is fired, it is forced into those grooves, which impart a spin to the bullet. The grooves are called rifling.
Ballistic spindrift is when the spin imparted on the bullet causes a drift in the direction the TOP of the bullet is spinning in.
The grooves in the barrel.
Because a spinning bullet travels in a straighter line, for further, than a bullet which is not spinning. So, in a word, "accuracy" is why a gun puts a spin on a bullet. Not all of the guns put spin on the bullet though. Those that do have rifled barrels(grooved on inside). There are also smooth bore guns that do not cause the projectile to spin.
Rifling causes the bullet to spin through the barrel and downrange. This spin stabilizes the bullet, allowing it to maintain a straight course to the target. Without the spin, accuracy would be dismal.
The grooves (rifling) cut into the barrel.
Rifling. The barrel is not smooth on the inside. There are small grooves spiraling down the barrel which makes the bullet spin. Nearly all shotguns do not have rifling in the barrel.
It makes the bullet spin when it is fired- much the same way a football spins in flight. The helps the bullet travel in a straight line, improving the accuracy of the gun.
It can. The rifling in the barrel causes the bullet to spin. This usually keeps the bullet moving relatively straight (because of gyroscopic stabilisation). However, as the bullet slows down at longer ranges, the spinning can cause it to wobble and drift. This is called spin drift. Spin drift can be upwards, so yes, rifling can cause a bullet to go up, but only at extreme ranges.
It causes the bullet to spin which makes it go straighter.
A bullet fired from a gun
It has gravity pulling it down, inertia pushing it forward, the spin of the bullet causing it to curve VERY slightly, and air resistance slowing it down.