What likely caused circumferential burrs near the tip of a rifle bore?

The presence of circumferential burrs near the tip of a rifle bore is most commonly associated with the improper use of piloted crowning tools. When crowning a rifle barrel, it’s critical that the tool be used correctly and that the machining process is done with precision. If the crowning tool is misaligned, damaged, or used incorrectly, it can lead to uneven metal removal. This uneven finishing may produce burrs around the edge of the bore, specifically where the rifling ends and the bore transitions into the muzzle area. Proper crowning is essential for ensuring a clean exit of the projectile from the bore, impacting both accuracy and overall performance of the rifle.

Other factors, such as overheating during shooting or dirty barrels, might affect barrel life or accuracy but would not systematically produce circumferential burrs. Manufacturing defects could certainly lead to issues in the barrel, but the specific issue of burrs at the tip is directly linked to improper crowning practices.