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Which factory 308 Win
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<blockquote data-quote="Michael Eichele" data-source="post: 279995" data-attributes="member: 1007"><p>I think you missunderstood my post.</p><p></p><p>The standard for a while was 12x for 168's and 11.25 for the 175 based on the out dated greenhill methods.</p><p></p><p>The newer and better methods of choosing twists will show you 12x for 175-180 and 13 for 168's. This corosponds well with real world reults.</p><p></p><p>I was just trying to illustrate to you why many shooters tell you 12x for 168. These are old standards and overkill.</p><p></p><p>As far as reading up on stability factors, I am not sure where to point you for reading. There arent alot of references that go into detail about it, just little snippits here and there.</p><p></p><p>In short a stability factor is the gyroscopic stability of a spinning object such as a bullet. When the factor is less than 1.0-1.1 it is unstable. The goal is about 1.5. this allows room for changing elements such as very dense air that lowers stability factors a bit. You wouldnt want to develop a load in 70 degree air at 5000 feet that has a SF of 1.1and then go to alaska and hunt moose in 10 degree air at sea level. This would cause a SF of under 1.0 and subsequently you would be unstable and the bullet will never reach the traget straight on or with any degree of accuracy.</p><p></p><p>In a 12x barrel at 2650 FPS a 175 SMK has a 1.65 SF in standard air (59 degrees F and 29.92 BP) In -30 degrees F at sea level, it is still 1.36. </p><p></p><p>Again, if you say 175 is your max bullet, get the 12x. a 10x will give you more than 2.3. This will cause sleep issues as well as possible jacket concentricity imperfection issues.</p><p></p><p>If you want a program for calculating SF, send me your email and I can send you a couple of different calculators to help you see the difference.</p><p></p><p>Also, there is one factory rifle that uses a 11.25 twist. This is a 700 5R (milspec). Agian though, this twist works better with the 190-200's.</p></blockquote><p></p>
[QUOTE="Michael Eichele, post: 279995, member: 1007"] I think you missunderstood my post. The standard for a while was 12x for 168's and 11.25 for the 175 based on the out dated greenhill methods. The newer and better methods of choosing twists will show you 12x for 175-180 and 13 for 168's. This corosponds well with real world reults. I was just trying to illustrate to you why many shooters tell you 12x for 168. These are old standards and overkill. As far as reading up on stability factors, I am not sure where to point you for reading. There arent alot of references that go into detail about it, just little snippits here and there. In short a stability factor is the gyroscopic stability of a spinning object such as a bullet. When the factor is less than 1.0-1.1 it is unstable. The goal is about 1.5. this allows room for changing elements such as very dense air that lowers stability factors a bit. You wouldnt want to develop a load in 70 degree air at 5000 feet that has a SF of 1.1and then go to alaska and hunt moose in 10 degree air at sea level. This would cause a SF of under 1.0 and subsequently you would be unstable and the bullet will never reach the traget straight on or with any degree of accuracy. In a 12x barrel at 2650 FPS a 175 SMK has a 1.65 SF in standard air (59 degrees F and 29.92 BP) In -30 degrees F at sea level, it is still 1.36. Again, if you say 175 is your max bullet, get the 12x. a 10x will give you more than 2.3. This will cause sleep issues as well as possible jacket concentricity imperfection issues. If you want a program for calculating SF, send me your email and I can send you a couple of different calculators to help you see the difference. Also, there is one factory rifle that uses a 11.25 twist. This is a 700 5R (milspec). Agian though, this twist works better with the 190-200's. [/QUOTE]
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