What does a concentricity gauge help with in reloading?

A concentricity gauge is specifically designed to measure radial run out, which refers to the deviation of a bullet's axis from a perfectly straight line in relation to the cartridge case. This tool allows reloaders to assess how well the bullet is aligned within the cartridge case. A bullet that is not seated concentrically may exhibit inaccuracies during flight, leading to poor shooting performance. By using a concentricity gauge, reloaders can identify issues with bullet seating and make necessary adjustments to ensure better alignment, thereby improving overall accuracy and consistency.

The other options focus on different aspects of reloading. Measuring bullet weight helps ensure that all bullets used are of similar mass, which is important for consistency, but it does not address alignment. Ensuring consistent powder loads is vital for achieving uniform velocity and performance, but it does not involve the axial alignment of the bullet. Checking primer seating depth is important for ignition consistency and reliability but does not relate directly to the concentricity of the bullet within the case. Thus, the role of a concentricity gauge is uniquely tied to measuring radial run out, making it essential for achieving optimal accuracy in ammunition reloading.