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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet stability
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<blockquote data-quote="Laguna Freak" data-source="post: 1952029" data-attributes="member: 87188"><p>Thread Resurrection;</p><p></p><p>I'm resurrecting this 3-year-old thread in hope of gaining some new insight and well-reasoned answers to a central question I have regarding two respected online Sg calculators.</p><p></p><p>My quest for information was initiated yesterday after I started a thread in the Long Range Hunting forum seeking opinions about the applicability of Nosler's 142 gr Accubond Long Range bullet in a 26 inch 264 Win Mag barrel with 1 : 9 twist. While all of the responses were helpful, none of them were able to satisfactorily address a central question I had. This central question regards the delta in results that I received from Berger's Bryan Litz Twist Rate Stability Calculator vs JBM Ballistics' Miller/Courtney Sg Calculator. In short the delta between these two calculators is the difference between an Sg of 1.27 (Litz) and 1.651 (Miller/Courtney). Essentially no-go vs go.</p><p></p><p><strong>My question; Which is the "most accurate" calculator?</strong></p><p></p><p>I believe the answer lies in the relevance of the data collected by each calculator. Each calculator asks for the same input data parameters with the exception that Berger's Litz asks for Altitude (Drag coefficient), while JBM's Miller/Courtney asks for barometric pressure and length of plastic ballistic tip (Drag coefficient and CG parameters).</p><p></p><p>I've studied up a little bit and have developed a basic understanding of Sg and its influence on the elusive Sd, and their collective potential transonic stability implications.</p><p></p><p>I've begun to develop an opinion about which calculator I am inclined to believe is "most accurate". But I don't want to pollute the thought pool with my primordial opinion.</p><p></p><p>Which one do you think is the "most accurate" Sg calculator? </p><p>Why?</p><p></p><p>Thanks to everyone who plays along with a well-reasoned response.</p><p></p><p></p><p></p><p><strong>Berger Litz:</strong></p><p></p><p><span style="font-size: 22px"><strong>Stability Analysis</strong></span></p><div style="text-align: center">Your bullet is MARGINALLY STABLE.</div> <div style="text-align: center">Your bullet stability is marginal. You may shoot good groups under these conditions, but the BC of the bullet will not be optimized.</div> <div style="text-align: center"></div><p>SG = 1.27 Bullet BC (G1): 0.625 Adjusted BC for 1 in 9" Twist: 0.582 </p><p>Your BC is being compromised by:7%</p><p>Minimum Twist Recommended: 1 in 8.25"</p><p></p><p></p><p><strong>JBM Miller/Courtney:</strong></p><p></p><table style='width: 100%'><tr><td><table style='width: 100%'><tr><td>Stability</td><td></td><td></td><td></td></tr><tr><td>Input Data</td><td></td><td></td><td></td></tr><tr><td>Caliber:</td><td>0.264 in</td><td>Bullet Weight:</td><td>142.0 gr</td></tr><tr><td>Bullet Length:</td><td>1.450 in</td><td>Plastic Tip Length:</td><td>0.190 in</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>Muzzle Velocity:</td><td>3050.0 ft/s</td><td>Barrel Twist:</td><td>9.0 in</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>Temperature:</td><td>80.0 °F</td><td>Pressure:</td><td>29.59 in Hg</td></tr><tr><td>Output Data</td><td></td><td></td><td></td></tr><tr><td>Stability:</td><td>1.651</td><td></td><td></td></tr></table></td></tr><tr><td><table style='width: 100%'><tr><td>31-Jul-20 17:10, <a href="http://www.jbmballistics.com/" target="_blank">JBM</a>/<a href="http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi" target="_blank">jbmstab-5.1.cgi</a></td></tr></table></td></tr></table></blockquote><p></p>
[QUOTE="Laguna Freak, post: 1952029, member: 87188"] Thread Resurrection; I’m resurrecting this 3-year-old thread in hope of gaining some new insight and well-reasoned answers to a central question I have regarding two respected online Sg calculators. My quest for information was initiated yesterday after I started a thread in the Long Range Hunting forum seeking opinions about the applicability of Nosler’s 142 gr Accubond Long Range bullet in a 26 inch 264 Win Mag barrel with 1 : 9 twist. While all of the responses were helpful, none of them were able to satisfactorily address a central question I had. This central question regards the delta in results that I received from Berger’s Bryan Litz Twist Rate Stability Calculator vs JBM Ballistics’ Miller/Courtney Sg Calculator. In short the delta between these two calculators is the difference between an Sg of 1.27 (Litz) and 1.651 (Miller/Courtney). Essentially no-go vs go. [B]My question; Which is the “most accurate” calculator?[/B] I believe the answer lies in the relevance of the data collected by each calculator. Each calculator asks for the same input data parameters with the exception that Berger’s Litz asks for Altitude (Drag coefficient), while JBM’s Miller/Courtney asks for barometric pressure and length of plastic ballistic tip (Drag coefficient and CG parameters). I’ve studied up a little bit and have developed a basic understanding of Sg and its influence on the elusive Sd, and their collective potential transonic stability implications. I’ve begun to develop an opinion about which calculator I am inclined to believe is “most accurate”. But I don’t want to pollute the thought pool with my primordial opinion. Which one do you think is the “most accurate” Sg calculator? Why? Thanks to everyone who plays along with a well-reasoned response. [B]Berger Litz:[/B] [SIZE=6][B]Stability Analysis[/B][/SIZE] [CENTER]Your bullet is MARGINALLY STABLE. Your bullet stability is marginal. You may shoot good groups under these conditions, but the BC of the bullet will not be optimized. [/CENTER] SG = 1.27 Bullet BC (G1): 0.625 Adjusted BC for 1 in 9" Twist: 0.582 Your BC is being compromised by:7% Minimum Twist Recommended: 1 in 8.25" [B]JBM Miller/Courtney:[/B] [TABLE] [TR] [TD][TABLE] [TR] [TD]Stability[/TD] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD]Input Data[/TD] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD]Caliber:[/TD] [TD]0.264 in[/TD] [TD]Bullet Weight:[/TD] [TD]142.0 gr[/TD] [/TR] [TR] [TD]Bullet Length:[/TD] [TD]1.450 in[/TD] [TD]Plastic Tip Length:[/TD] [TD]0.190 in[/TD] [/TR] [TR] [TD][/TD] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD]Muzzle Velocity:[/TD] [TD]3050.0 ft/s[/TD] [TD]Barrel Twist:[/TD] [TD]9.0 in[/TD] [/TR] [TR] [TD][/TD] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD]Temperature:[/TD] [TD]80.0 °F[/TD] [TD]Pressure:[/TD] [TD]29.59 in Hg[/TD] [/TR] [TR] [TD]Output Data[/TD] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD]Stability:[/TD] [TD]1.651[/TD] [TD][/TD] [TD][/TD] [/TR] [/TABLE][/TD] [/TR] [TR] [TD][TABLE] [TR] [TD]31-Jul-20 17:10, [URL='http://www.jbmballistics.com/']JBM[/URL]/[URL='http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi']jbmstab-5.1.cgi[/URL][/TD] [/TR] [/TABLE][/TD] [/TR] [/TABLE] [/QUOTE]
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