Experienced shooters know that accuracy is degraded when the bullet is misaligned with the cartridge case centerline and the bore axis. Bullets entering the rifling at an angle will show a phenomenon known as “in-bore yaw.” Well-studied by American Rifleman Ballistics Editor William C. Davis and his associate, Charles Fagg, in-bore yaw can contribute significantly to group dispersion. Unfortunately, even the best ammunition may exhibit an undesirable degree of bullet misalignment or runout—generally, more than 0.002-0.003 inches. Hornady’s Lock-N-Load Concentricity Tool not only measures bullet misalignment on virtually any cartridge, but also corrects it.
The primary parts are the rigid aluminum frame, cartridge and bullet spindles, and a moveable cradle that contains both the supplied dial indicator and the nylon-tipped straightening thumbscrew. Three different bullet spindles are provided to accommodate varying bullets noses. Also included are comprehensive instructions.
Setting it up is simple and quick. First the cartridge spindle is adjusted for the length of the loaded round. The tool comes with a bullet spindle already mounted; if necessary for a different bullet tip, a new spindle is threaded onto the spring-loaded ball knob. Finally, the dial indicator is installed in the cradle and its lock screw is tightened.
To use the unit, the case head is first fit into the cartridge spindle, whose conical recess accepts heads of any size and centers them. Next, the ball knob and the attached bullet spindle are pulled to the right to insert the bullet tip into the spindle. The cradle is moved until the dial indicator tip compresses against the bullet just forward of the case mouth, the cartridge is rotated in the Tool, and the degree of runout is read off the dial. Cartridges with more than about 0.003 inches of variance should be culled for practice or sighting-in.
Correcting a misaligned bullet is also simple. The cartridge is rotated to put the “high point” of misalignment directly under the nylon-tipped straightening thumb screw, located directly opposite to the dial indicator tip. The screw is tightened against the bullet until the cartridge is straightened, as indicated by the dial indicator. The cartridge is then rotated again to determine how much runout still exists, and the process is repeated as necessary.
Testing with 6.5 Creedmoor and .308 Win. target rifles showed that cartridges with 0.002 inches or less runout grouped measurably better than those with 0.006 inches or more. Just as significantly, shooting tests at 600 yards showed that cartridges straightened with the Concentricity Tool produced none of the flyers experienced with unstraightened ammunition.
To be sure, correcting bullet misalignment will not produce the same performance improvement in all guns. However, any reasonably accurate rifle should group noticeably better with ammunition sorted and straightened in the Hornady Lock-N-Load Concentricity Tool, making it highly useful to precision shooters.