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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability Formula for Aluminum Tipped Bullets (Spreadsheet linked)
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<blockquote data-quote="Michael Courtney" data-source="post: 994882" data-attributes="member: 28191"><p>I do not think we have measured the depth of the open tips on the Berger 75 or Nosler CC 77. You really need accurate numbers for all the fields in the spreadsheet to get a reliable prediction within the accuracy of the formula. For the numbers I have for the 75 AMAX, the plastic tipped formula gives Sg close to 1.3 at sea level under standard conditions in a 1 in 9" twist barrel. You'll be in trouble if the barrel is really 1 in 9.25" or on a cold winter day.</p><p></p><p>If I had personally measured the bullets and I was confident in the twist rate of the barrel manufacturer and I knew the environmental conditions I intended to shoot in, I would not hesitate to buy a barrel where the formula predicted an SG of 1.5. Unless you're at a pretty good elevation, I don't think I can recommend a 1 in 9" twist for the 75 AMAX. </p><p></p><p>At high elevations, we've shot the 69 grain NCC from a 1 in 12" twist with a SG close to 1.5 and BC of 0.290. The "lost" BC is more likely due to Nosler's propensity for inflating BC claims rather than insufficiency in stability.</p></blockquote><p></p>
[QUOTE="Michael Courtney, post: 994882, member: 28191"] I do not think we have measured the depth of the open tips on the Berger 75 or Nosler CC 77. You really need accurate numbers for all the fields in the spreadsheet to get a reliable prediction within the accuracy of the formula. For the numbers I have for the 75 AMAX, the plastic tipped formula gives Sg close to 1.3 at sea level under standard conditions in a 1 in 9" twist barrel. You'll be in trouble if the barrel is really 1 in 9.25" or on a cold winter day. If I had personally measured the bullets and I was confident in the twist rate of the barrel manufacturer and I knew the environmental conditions I intended to shoot in, I would not hesitate to buy a barrel where the formula predicted an SG of 1.5. Unless you're at a pretty good elevation, I don't think I can recommend a 1 in 9" twist for the 75 AMAX. At high elevations, we've shot the 69 grain NCC from a 1 in 12" twist with a SG close to 1.5 and BC of 0.290. The "lost" BC is more likely due to Nosler's propensity for inflating BC claims rather than insufficiency in stability. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability Formula for Aluminum Tipped Bullets (Spreadsheet linked)
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