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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability: Fine Points to be Aware Of
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<blockquote data-quote="Hugnot" data-source="post: 2633813" data-attributes="member: 115658"><p>The Miller Sg estimator:</p><p></p><p>[ATTACH]399230[/ATTACH]</p><p></p><p></p><p></p><p>The Berger Stability Calculator:</p><p></p><p>[ATTACH]399228[/ATTACH]</p><p></p><p></p><p></p><p>Altitude & Barometric Pressure:</p><p></p><p>[ATTACH]399231[/ATTACH]</p><p></p><p></p><p></p><p></p><p>Running my home-made spreadsheet using the Miller method & comparing the Sg estimates with the Berger stability analysis for the Berger 85.5 .224 bullet, 7.7 twist, 3050 fps, 89 deg, 0 sea level, I produced a Sg of 1.43 with my home-made number fixer & the Berger Sg analyst stuff produced a Sg of 1.42. Berger than stated the Sg of 1.42 was "marginal".</p><p></p><p>Going into this the gyroscopic effect:</p><p></p><p><strong>"Gyroscopic motion is the tendency of a rotating object to maintain the orientation of its rotation</strong>. A rotating object possesses angular momentum and this momentum must be conserved. The object will resist any change in its axis of rotation, as a change in orientation will result in a change in angular momentum."</p><p></p><p>In addition - precession - coning motion:</p><p></p><p>"Torque-induced <a href="https://www.bing.com/ck/a?!&&p=be6c5843d00a119bJmltdHM9MTY2NTAxNDQwMCZpZ3VpZD0wNzc5YTQxMS1mYWI1LTY0MTYtMzFiZi1iNjI0ZmI5ODY1YzYmaW5zaWQ9NTUxMQ&ptn=3&hsh=3&fclid=0779a411-fab5-6416-31bf-b624fb9865c6&u=a1L3NlYXJjaD9xPVByZWNlc3Npb24mZmlsdGVycz1zaWQlM2E1YjhhNDM0ZC0xZjBiLTgwOGEtY2M3MS04OTlmMGU0MzU3YmMmZm9ybT1FTlRMTks&ntb=1" target="_blank">precession</a> (gyroscopic precession) is the<strong> phenomenon in which the axis of a spinning object</strong> (e.g., a gyroscope) describes a cone in space when an external torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession."</p><p></p><p>Like move 90 degrees from direction force applied then rotating point describes a cone.</p><p></p><p>The Miller Sg estimator process applied by my home-made Sg number fixer & the Berger Sg analyzer accepts data like twist, velocity, pressure, temp. Looking at velocity & twist: a ratio of diameter H131/ twist H135 and a comparison of velocity H136 - 2800 (a standard) is used.</p><p></p><p>The rotational stuff like RPM's would be regarded as constant over the bullet's relatively short TOF. Per Berger, factors like twist, velocity, & air density would affect stability, like lower Sg values and less than optimum performance, less than the optimum BC.</p><p></p><p>I like the Hornady 4DOF ballistic calculator, it shows Sg's increasing down range. Initial Sg's are affected by MV & twist rate. Features like aerodynamic jump & spin drift are included. "The barrel twist, velocity, and air density will determine the muzzle <strong>Sg</strong> along with other projectile properties included in the projectile file."</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2633813, member: 115658"] The Miller Sg estimator: [ATTACH alt="Screenshot (475).png"]399230[/ATTACH] The Berger Stability Calculator: [ATTACH alt="Screenshot (472).png"]399228[/ATTACH] Altitude & Barometric Pressure: [ATTACH alt="Screenshot (471).png"]399231[/ATTACH] Running my home-made spreadsheet using the Miller method & comparing the Sg estimates with the Berger stability analysis for the Berger 85.5 .224 bullet, 7.7 twist, 3050 fps, 89 deg, 0 sea level, I produced a Sg of 1.43 with my home-made number fixer & the Berger Sg analyst stuff produced a Sg of 1.42. Berger than stated the Sg of 1.42 was "marginal". Going into this the gyroscopic effect: [B]"Gyroscopic motion is the tendency of a rotating object to maintain the orientation of its rotation[/B]. A rotating object possesses angular momentum and this momentum must be conserved. The object will resist any change in its axis of rotation, as a change in orientation will result in a change in angular momentum." In addition - precession - coning motion: "Torque-induced [URL='https://www.bing.com/ck/a?!&&p=be6c5843d00a119bJmltdHM9MTY2NTAxNDQwMCZpZ3VpZD0wNzc5YTQxMS1mYWI1LTY0MTYtMzFiZi1iNjI0ZmI5ODY1YzYmaW5zaWQ9NTUxMQ&ptn=3&hsh=3&fclid=0779a411-fab5-6416-31bf-b624fb9865c6&u=a1L3NlYXJjaD9xPVByZWNlc3Npb24mZmlsdGVycz1zaWQlM2E1YjhhNDM0ZC0xZjBiLTgwOGEtY2M3MS04OTlmMGU0MzU3YmMmZm9ybT1FTlRMTks&ntb=1']precession[/URL] (gyroscopic precession) is the[B] phenomenon in which the axis of a spinning object[/B] (e.g., a gyroscope) describes a cone in space when an external torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession." Like move 90 degrees from direction force applied then rotating point describes a cone. The Miller Sg estimator process applied by my home-made Sg number fixer & the Berger Sg analyzer accepts data like twist, velocity, pressure, temp. Looking at velocity & twist: a ratio of diameter H131/ twist H135 and a comparison of velocity H136 - 2800 (a standard) is used. The rotational stuff like RPM's would be regarded as constant over the bullet's relatively short TOF. Per Berger, factors like twist, velocity, & air density would affect stability, like lower Sg values and less than optimum performance, less than the optimum BC. I like the Hornady 4DOF ballistic calculator, it shows Sg's increasing down range. Initial Sg's are affected by MV & twist rate. Features like aerodynamic jump & spin drift are included. "The barrel twist, velocity, and air density will determine the muzzle [B]Sg[/B] along with other projectile properties included in the projectile file." [/QUOTE]
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