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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6mm Creedmoor barrel twist?
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<blockquote data-quote="Hugnot" data-source="post: 3095296" data-attributes="member: 115658"><p>Go for the 110 A-Tip in the 7 twist, if it's OK for 115's it will work for the pricy & trendy A-Tip.</p><p></p><p>[ATTACH]567858[/ATTACH]</p><p></p><p>Bullet length data from JBM. The A-Tip is 1.307 inches long & has a .160 inch long aluminum tip. Since aluminum weighs more (greater density) than plastic, I included it in the bullet OAL.</p><p></p><p>Now & then I gets to buy partial boxes of bullets real cheap that don't shoot too good from other shooters, like sideways bullet holes or substandard trajectories & poor accuracy at long ranges due to BC degradation (not flying good, like wobbling) indicated by low Sg values.</p><p></p><p>A simple Sg analysis from Berger:</p><p></p><p>[URL unfurl="true"]https://bergerbullets.com/twist-rate-calculator/[/URL]</p><p></p><p>and</p><p></p><p>[ATTACH]567863[/ATTACH]</p><p></p><p>Here the bullet wizards indicate doubts regarding optimum accuracy with bullet having Sg values in excess of 2.0. I think this has some validity & prefer to not get into super fast twist barrels that would optimize bullet use to real long pointy bullets. Why go for an excessive fast twist when not needed. Sort of looks like bullet trends and barrel twist rates are determined by ignoring analysis.</p><p></p><p>In addition the US Government, like the DOD, having access to huge amounts of funding has determined acceptable Sg value ranges.</p><p></p><p>"<em>A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets.</em>"</p><p></p><p>Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets.</p><p>The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. An additional qualifier would bullet form factor, obtained by dividing the bullet</p></blockquote><p></p>
[QUOTE="Hugnot, post: 3095296, member: 115658"] Go for the 110 A-Tip in the 7 twist, if it's OK for 115's it will work for the pricy & trendy A-Tip. [ATTACH alt="Screenshot (903).png"]567858[/ATTACH] Bullet length data from JBM. The A-Tip is 1.307 inches long & has a .160 inch long aluminum tip. Since aluminum weighs more (greater density) than plastic, I included it in the bullet OAL. Now & then I gets to buy partial boxes of bullets real cheap that don't shoot too good from other shooters, like sideways bullet holes or substandard trajectories & poor accuracy at long ranges due to BC degradation (not flying good, like wobbling) indicated by low Sg values. A simple Sg analysis from Berger: [URL unfurl="true"]https://bergerbullets.com/twist-rate-calculator/[/URL] and [ATTACH alt="Screenshot (904).png"]567863[/ATTACH] Here the bullet wizards indicate doubts regarding optimum accuracy with bullet having Sg values in excess of 2.0. I think this has some validity & prefer to not get into super fast twist barrels that would optimize bullet use to real long pointy bullets. Why go for an excessive fast twist when not needed. Sort of looks like bullet trends and barrel twist rates are determined by ignoring analysis. In addition the US Government, like the DOD, having access to huge amounts of funding has determined acceptable Sg value ranges. "[I]A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets.[/I]" Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets. The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. An additional qualifier would bullet form factor, obtained by dividing the bullet [/QUOTE]
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6mm Creedmoor barrel twist?
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