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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Berger Twist Rate Stability Calculator (need help)
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<blockquote data-quote="Hugnot" data-source="post: 2024495" data-attributes="member: 115658"><p>Taking a look at this:</p><p></p><p>The 87 VMax @ 3250</p><p></p><p>The formula gives a blow up velocity of 3392 and change for a 87 VMax with a 8 twist. Bullet construction and jacket thickness varies, does the subject method consider this aspect? In any event, my 3250 fps velocities are 142 fps under the formula derived blow up limit. When shot thru my old 8 twist 6mm AI barrel at over 3400 (real close to 3392) they did not blow up. Hornady's notes their .224 SX bullets have velocity limits of 3,500 fps but do not specify twist rate. </p><p></p><p>Looking at a 53 .224, VMax shot from a 7.7 twist comes up with a blow up velocity of 3313 & change. This is a thin jacket bullet. They don't blow up at 3600 or so thru my .22-.250, 7.7 twist. An extremely smooth well lapped, 5R 7.7 twist McGowen barrel.</p><p></p><p>My old 10 twist .22-250 got about 4,000 fps with the 40 grain .224 VMax; the .224 blow up limit for a 10 twist is 4302 fps. Well within formula limits. Terrific performance on small rodents. The 10 twist barrel could launch a 68 grain Hornady HPBT and could hit silhouette chickens at 880 on a nice warm day despite having a Sg of 1.06. The nice smart gunsmith suggested going with a 10 twist.</p><p></p><p>In a recent article about the 6mm-06 in the October 2020, in <em>Handloader</em> magazine, bottom left page 36, gives a velocity of <u>3664</u> for the 87 VMax, 6mm-06, 8 twist, 6mm-06, with 52.5 grains of RL17. Group size at 100 was shown at .58 inches, 3 shot. I will soon attempt to duplicate this with my 8 twist 6mm-06. 3664 fps is well over the 3392 limit. Will I see gray smoke? Can't wait to report back.</p><p></p><p>I don't understand the how & why of constants (1.389, 238.095 & 290) used in the formula. Are there any references to this?</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2024495, member: 115658"] Taking a look at this: The 87 VMax @ 3250 The formula gives a blow up velocity of 3392 and change for a 87 VMax with a 8 twist. Bullet construction and jacket thickness varies, does the subject method consider this aspect? In any event, my 3250 fps velocities are 142 fps under the formula derived blow up limit. When shot thru my old 8 twist 6mm AI barrel at over 3400 (real close to 3392) they did not blow up. Hornady's notes their .224 SX bullets have velocity limits of 3,500 fps but do not specify twist rate. Looking at a 53 .224, VMax shot from a 7.7 twist comes up with a blow up velocity of 3313 & change. This is a thin jacket bullet. They don't blow up at 3600 or so thru my .22-.250, 7.7 twist. An extremely smooth well lapped, 5R 7.7 twist McGowen barrel. My old 10 twist .22-250 got about 4,000 fps with the 40 grain .224 VMax; the .224 blow up limit for a 10 twist is 4302 fps. Well within formula limits. Terrific performance on small rodents. The 10 twist barrel could launch a 68 grain Hornady HPBT and could hit silhouette chickens at 880 on a nice warm day despite having a Sg of 1.06. The nice smart gunsmith suggested going with a 10 twist. In a recent article about the 6mm-06 in the October 2020, in [I]Handloader[/I] magazine, bottom left page 36, gives a velocity of [U]3664[/U] for the 87 VMax, 6mm-06, 8 twist, 6mm-06, with 52.5 grains of RL17. Group size at 100 was shown at .58 inches, 3 shot. I will soon attempt to duplicate this with my 8 twist 6mm-06. 3664 fps is well over the 3392 limit. Will I see gray smoke? Can't wait to report back. I don't understand the how & why of constants (1.389, 238.095 & 290) used in the formula. Are there any references to this? [/QUOTE]
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Berger Twist Rate Stability Calculator (need help)
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