JBM Small Arms Ballistics
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A new topic, Elevation, has been added. It shows the differences in trajectories when zeroing at different atmospheric conditions and how to calculate a trajectory for different atmospheric conditions.


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JBM - Calculations - Drag/Twist Input

This calculator provides the bullet drag and stability (not Greenhill's formula) based on bullet dimensions. It is based on Bob McCoy's McDrag and McGyro. Explanation of terms.

Caliber (0.1-2.0 inches) [0.224]
Nose Length (1.2-5.5 calibers) [3.000]
Meplat Diameter (<0.35 calibers) [0.000]
Ogive Radius (1-1000 calibers) [18.0]
Nose Type [Secant]
Boattail Length (<2 calibers) [1.000]
Base Diameter (<1 caliber) [0.754]
Total Length (2.5-10 calibers) [5.480]
Rotating Band Diameter (1.0-1.06 calibers) [1.000]
Weight (10-15000 grains) [55]
Specific Gravity (2.0-20.0) [10.7]
Drag Function [G1]
Barrel Twist (2.0-100.0) [10.0]

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JBM Small Arms Ballistics. Last update 22 April 2008, Copyright © 1996-2008 JBM [V]