Reviewers needed: Aerodynamic Drag and Gyroscopic Stability
Please send an email to [email protected] if you'd like to review the full paper.
Abstract: This paper describes the effects on aerodynamic drag on rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that the bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here by comparing measured ballistic coefficients with gyroscopic stabilities computed with the Miller Twist Rule for nearly solid metal bullets with uniform density and computed with the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 ± 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relative accuracy of the twist formulas used to compute Sg. It may be used to test the applicability of existing twist formulas to given bullet designs and to evaluate the accuracy of alternate formulas in cases where the existing twist formulas are not as accurate.
Please send an email to [email protected] if you'd like to review the full paper.
Abstract: This paper describes the effects on aerodynamic drag on rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that the bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here by comparing measured ballistic coefficients with gyroscopic stabilities computed with the Miller Twist Rule for nearly solid metal bullets with uniform density and computed with the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 ± 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relative accuracy of the twist formulas used to compute Sg. It may be used to test the applicability of existing twist formulas to given bullet designs and to evaluate the accuracy of alternate formulas in cases where the existing twist formulas are not as accurate.
