Question 1

What size neck bushing do I need?

Accepted Answer

For Method A (loaded-round measurement), subtract your desired neck tension (typically 0.002″–0.003″) from the measured outside diameter of the loaded neck and round to the nearest 0.001″. For Method B (unloaded components), add twice the neck-wall thickness to the bullet diameter and subtract 0.001″ for brass spring-back.

Question 2

What is neck tension and how much do I need?

Accepted Answer

Neck tension is the interference fit between the brass neck and the bullet — the amount of "squeeze" holding the bullet in place. For most centerfire precision rifle loads, 0.002″ is a typical starting point. Heavier loads, magnum calibers, and tube-magazine actions often run 0.003″. F-Class and benchrest shooters sometimes experiment down to 0.0015″ for best accuracy.

Question 3

Do I measure the loaded round or the brass?

Accepted Answer

Either works. Measuring a loaded round is easier and accounts for any variation in your actual brass + bullet combination. Measuring components is useful when you don't have a sample loaded round yet — like when setting up a new cartridge for the first time.

Question 4

Why subtract 0.001″ for spring-back?

Accepted Answer

Brass is elastic. After you size the neck down with a bushing, the metal springs back slightly — typically about 0.001″. So the final neck inside diameter ends up slightly larger than the bushing. This calculator bakes that offset in for the component-based method, so the output is the ready-to-order bushing size.

Question 5

Should I order the exact size, or one above and one below?

Accepted Answer

Experienced handloaders often order all three: the calculated size, one 0.001″ tighter, and one 0.001″ looser. That way you can experiment with tension in load development without waiting on shipping. The calculator displays all three for convenience.

Neck Bushing Calculator