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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Twist rate, how fast is too fast?
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<blockquote data-quote="FEENIX" data-source="post: 2458727" data-attributes="member: 14204"><p>You must be higher than my altitude to get an SG of 1.69, i.e., 5000'. Please double-check your inputs for your calculation. Using 150 ABLR's G1 of .592, OAL of 1.39" at my altitude of 3300', and MV of 3000 FPS:</p><p></p><p>[ATTACH=full]345254[/ATTACH]</p><p></p><p>You should be able the propel the 150 ABLR in the 3100+ FPS with your .270 WBTY without any issues.</p><p></p><p></p><p>Berger recommends the barrel twist rate for the 170 is 1:9" or faster. Using Berger 170's G1 of .662, OAL of 1.49" at my altitude of 3300', and MV of 2900 FPS:</p><p></p><p>[ATTACH=full]345255[/ATTACH]</p><p></p><p>My .270 AI has a 30" 1:8" if I use the same 170 Berger information:</p><p></p><p>[ATTACH=full]345257[/ATTACH]</p><p></p><p>NOTE: I should have used MV 2800 FPS instead of 2900 FPS. SG at 2800 FPS with the 170; 1:10" = 1.37, 1:8" = 2.15.</p></blockquote><p></p>
[QUOTE="FEENIX, post: 2458727, member: 14204"] You must be higher than my altitude to get an SG of 1.69, i.e., 5000'. Please double-check your inputs for your calculation. Using 150 ABLR's G1 of .592, OAL of 1.39" at my altitude of 3300', and MV of 3000 FPS: [ATTACH type="full" alt="ABLR 150 in 10.jpg"]345254[/ATTACH] You should be able the propel the 150 ABLR in the 3100+ FPS with your .270 WBTY without any issues. Berger recommends the barrel twist rate for the 170 is 1:9" or faster. Using Berger 170's G1 of .662, OAL of 1.49" at my altitude of 3300', and MV of 2900 FPS: [ATTACH type="full" alt="Berger 170 in 10.jpg"]345255[/ATTACH] My .270 AI has a 30" 1:8" if I use the same 170 Berger information: [ATTACH type="full" alt="Berger 170 in 8.jpg"]345257[/ATTACH] NOTE: I should have used MV 2800 FPS instead of 2900 FPS. SG at 2800 FPS with the 170; 1:10" = 1.37, 1:8" = 2.15. [/QUOTE]
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Twist rate, how fast is too fast?
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