| Rifling |
Rifling utilizes the gyroscopic affect to stabilize a bullet while in flight. A rifled barrel has lands and grooves that spiral down the length of the bore. As the bullet travels down the barrel it is spun by these lands and grooves, imparting an angular momentum. This angular momentum makes the bullet resistant to change its axis of rotation and therefore stabilizes its flight similar to how a spinning top remains balanced.
The bullet fits tightly in the barrel and the rifling actually cuts serrations on the surface of the bullet. Soft metals such as lead and copper are used to prevent damage to the rifling. Most bullets have a core of lead and are jacketed with copper but can be solid lead or solid copper or even have a mild steel or hardened steel/tungsten core in the case of armor piercing rounds.
As the bullet flies through the air its axis of rotation stays "relatively" constant. This will be elaborated in Spindrift.