You've sorted your brass by weight. You've measured powder charges to the kernel. Your seating depth is dialed to within a thousandth of an inch. But if your bullets aren't sitting straight in the case, if there's runout, all that precision work can be undermined before the round ever reaches the chamber.
Bullet runout, also called concentricity error, is one of the most talked-about accuracy variables in precision reloading, yet it often gets less attention than seating depth or powder charge. This guide explains what runout is, why it matters, how to measure it, what causes it, and how to minimize it using inline seating equipment.
What Is Bullet Runout?
Runout refers to how far off-center a bullet is relative to the axis of the cartridge case. In a perfectly concentric round, the bullet's centerline aligns exactly with the centerline of the case. In the real world, slight misalignment exists in virtually every round, the question is how much.
Runout is typically measured in thousandths of an inch (TIR, Total Indicator Reading) using a concentricity gauge or a dial indicator mounted in a fixture that rotates the cartridge. A reading of 0.001" TIR means the bullet is off-center by half a thousandth.
Why Does Runout Affect Accuracy?
When a bullet isn't seated straight, several things happen upon firing that negatively affect accuracy:
- The bullet enters the rifling at a slight angle, creating uneven engraving
- Asymmetric forces are applied as the bullet travels down the bore
- The bullet may exit the muzzle with yaw or tilt
At short distances this may be minimal, but at 600 or 1,000 yards, the effect compounds, contributing to vertical and horizontal dispersion.
For competitive long-range shooters, concentricity is often the difference between a clean run and a dropped point. For hunters, it can mean the difference between a clean kill and a wounded animal at extended distances.
Acceptable Runout Tolerances
General guidelines used by precision reloaders:
- 0.001" TIR or less: Excellent, competition-level precision
- 0.001" to 0.002": Good, suitable for most precision shooting
- 0.002" to 0.003": Acceptable for hunting and general use
- Over 0.003": Noticeable accuracy degradation
Factory ammunition typically runs between 0.002" and 0.005" TIR. This is one of the core reasons that carefully prepared handloads can outperform factory rounds, the reloader has direct control over every variable that contributes to concentricity.
How to Measure Runout
To measure runout you need a concentricity gauge, a fixture that holds a cartridge and allows you to rotate it while a dial indicator touches the bullet near the tip. Some reloaders use a V-block and dial indicator setup on a surface plate; purpose-built concentricity gauges offer more convenience and repeatability.
Measuring procedure:
- Place the loaded cartridge in the gauge, with the indicator touching the bullet shank (not the tip, which can have slight tip deformities that give false readings)
- Rotate the cartridge one full revolution while watching the indicator
- Record the Total Indicator Reading: the difference between the highest and lowest values
- Measure several rounds from the same batch to understand batch-level consistency, not just individual outliers
What Causes Runout?
Die Alignment
Traditional threaded sizing and seating dies can introduce runout if the die body isn't perfectly aligned with the press ram. Thread engagement itself involves slight side-play that can translate to bullet misalignment. This is particularly relevant in seating dies, if the bullet isn't guided into the case in a perfectly straight line, runout is the result.
Case Neck Uniformity
Uneven neck walls, where one side of the neck is thicker than the other, cause the bullet to be pushed off-center during seating. The thicker side of the neck offers more resistance, deflecting the bullet slightly toward the thinner side. Neck turning, which removes material from the outside of the neck to create uniform wall thickness, is the solution for cases with severe neck wall variation.
Seating Die Design
The geometry of the seating plug matters. How a seating die that contacts the bullet, or one that uses a short alignment section, offers less guidance during seating and is more prone to introducing runout, especially with boat-tail bullets whose tapered base provides minimal registration surface.
Case Mouth Condition
A case mouth that's not uniformly chamfered, or that has irregularities from trimming, can deflect a bullet during seating. Consistent deburring and chamfering, using a quality tool that cuts evenly, is an often-overlooked contributor to low runout.
How Inline Seating Dies Reduce Runout
Inline seating dies provide a more consistent alignment method compared to traditional threaded dies.
L.E. Wilson inline chamber-type seating dies align the case and bullet within the die body itself, rather than relying on press alignment. This reduces the chance of off-axis seating.
Precision shooters often see runout reduced from 0.003"+ down to 0.001" or less when switching to inline seating systems. For long-range competition, that improvement is significant and repeatable.
Sorting and Correcting Rounds with High Runout
Even with proper setup, some rounds will have higher runout.
- Some reloaders gently correct runout manually (advanced technique)
- More commonly, rounds are sorted by concentricity
- Best rounds are used for competition or critical shooting
- Higher runout rounds are used for practice
Sorting adds minimal time but can significantly improve performance consistency.
Conclusion
Runout is a measurable accuracy variable that becomes increasingly important at longer distances. Controlling it requires proper case prep, consistent technique, and the right equipment.
The combination of uniform brass preparation and inline seating technology from L.E. Wilson provides one of the most effective ways to minimize runout and improve overall accuracy.
Measure it, control it, and your groups will reflect the difference.
