Cannelure
A circumferential groove rolled or cut into a bullet's jacket. Provides a crimp seat and helps lock the bullet to a specific seating depth.
Cannelures are common on hunting and military bullets. The brass case is crimped into the groove, anchoring the bullet so recoil doesn’t push it deeper into the case during magazine cycling.
Most precision match bullets don’t have cannelures. They’re designed for tight tolerances and consistent seating depth without crimping. Crimping a non-cannelured bullet usually degrades accuracy, so most handloaders skip the crimp there.