A case neck with irregular thickness can add inconsistent tension to the bullet and ruin your precision. Unfortunately, even newly produced brass can vary in thickness from one lot to another.
The outside of the cartridge is ideally aligned in a concentric circle around the axis. Using the wrong shell holder or improperly indexing can alter the “concentricity” of a case. Concentricity is used to identify a number of issues that affect ammunition loaded for accuracy.
Variations of .0015″ and greater in the case’s neck, shoulder and body indicate correction by fire forming to your rifle chamber, resizing or outside neck turning to ensure the most consistent performance. Upgrading to our Bench Rest® Seater Dies may also improve concentricity.
The angle and position at which the bullet enters the bore, commonly known as total indicated (bullet) runout, or TIR, is ideally zero. Most shooters limit their TIR to no more than .002” to .005”, depending on where they measure along the cartridge. “Tipped” bullets – with high TIR – are certain to shoot off target.
Variations of at least .004″ generally also call for correction by fire forming to your rifle chamber, resizing or outside neck turning to ensure the most consistent performance. Upgrading to Bench Rest Seater Dies may also lower TIR.