Rifling
The spiral grooves inside a barrel that spin the bullet for gyroscopic stability. Most precision barrels are cut, button-formed, or hammer-forged.
Cut rifling: a single-point tool makes one pass at a time. The process is slow and expensive, but it delivers exceptional precision. Most match-grade barrels (Bartlein, Krieger, Brux) use it.
Button rifling: a hardened carbide button is pulled through the bore, displacing metal to form the lands and grooves. Faster than cutting, still excellent quality at a lower price.
Hammer-forged: a mandrel is hammered against the barrel exterior, swaging the rifling into the bore. Very durable, used by most factory rifle barrels.