Barrel Twist Rate Calculator
Calculate optimal barrel twist rate from bullet length and diameter using the Greenhill formula. Accounts for bullet material density.
Inputs
in
in
Results
Recommended Twist (1:X)
11.5"
Greenhill C=15011.5"
Greenhill C=180 (>2800fps)13.8"
Length/Diameter Ratio4.03
Recommended Twist11.48
How to Use This Calculator
- Enter Bullet Length, Bullet Diameter, and Bullet Specific Gravity.
- Review the Recommended Twist (1:X) () result.
- Use Greenhill C=150 () and Greenhill C=180 (>2800fps) () to inform your decision.
- Use the chart to visualize the results and explore different scenarios by adjusting inputs.
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