If you’ve ever wanted a quick way to calculate neck sizer bushing diameter, this is the calculator for you! Just enter the information below in the text fields, click the “Calculate” button, and you’ll have a suggested neck bushing diameter to use for your sizer die.
Neck Bushing Diameter Calculator
The Math
In case you’re interested, here’s the calculation being performed:
- Bushing diameter (inches, as calculated) = BD
- Bullet diameter (inches, as measured) = D
- Average case neck thickness (inches, as measured) = T
- Bullet tension press fit = BT = 0.001″ (can customize to your preference)
- Brass spring back factor = SBF = 0.001″ (this can vary, especially when annealing is involved)
The formula is: BD = D + 2 x T – BT – SBF
Simplified, this becomes: BD = D + 2 x T – 0.002″ (default values for neck tension and spring back)
Example
The default values for the calculator above yield the following:
BD = 0.308″ + 2 x 0.014″ – 0.002″ = 0.334″
I hope this calculator is helpful for you!
Thanks,
Gavin
