I use a Bonanza COAX measuring tool that you have to supply a separate dial indicator for. It measures bullet runout; that is, the amount the bullet tip diverges from the central axis. On cases with bad runout, you can see it by rolling them across a flat table and watching the bullet tips wobble as they roll.
In one experiment with my .223 Ruger Varmint rifle, 7x24x50 varmint scope, the cartridges that had .001" runout, shot 1" approx. groups at 100 yds. Runout of .002" shot 2" groups, and .003" runout, 3" groups. This is of course within a deviation of around 1/4" for holding error.
Cartridges with well under .001" runout shot groups with holes touching.
A Lee neck sizing die on my 30-06 produced cartridges with almost no runout; maybe .0005" or less. The rifle shot accordingly.
I found that this eccentricity or runout was the largest factor in causing flyers or just poor accuracy. Of course that is after tuning the rifle and good bullet Manufacturer selection.
The theory is, a cartridge chambered in the rifle where the bullet tip is not centered, will move down the barrel with it's center axis of mass off center. The pressure in the chamber causing the bullet to become a plastic-like mass.
The bullet emerges from the muzzle with the axis center of mass different than it was in the barrel causing it to divert from it's aimed point.
Hope that is clear.
In one experiment with my .223 Ruger Varmint rifle, 7x24x50 varmint scope, the cartridges that had .001" runout, shot 1" approx. groups at 100 yds. Runout of .002" shot 2" groups, and .003" runout, 3" groups. This is of course within a deviation of around 1/4" for holding error.
Cartridges with well under .001" runout shot groups with holes touching.
A Lee neck sizing die on my 30-06 produced cartridges with almost no runout; maybe .0005" or less. The rifle shot accordingly.
I found that this eccentricity or runout was the largest factor in causing flyers or just poor accuracy. Of course that is after tuning the rifle and good bullet Manufacturer selection.
The theory is, a cartridge chambered in the rifle where the bullet tip is not centered, will move down the barrel with it's center axis of mass off center. The pressure in the chamber causing the bullet to become a plastic-like mass.
The bullet emerges from the muzzle with the axis center of mass different than it was in the barrel causing it to divert from it's aimed point.
Hope that is clear.