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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
marginal stability
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<blockquote data-quote="PNWdude67" data-source="post: 1911238" data-attributes="member: 110615"><p>Work up a load that is stable at the lowest elevation you shoot. The 1.5 stability guideline is just that, and when a bullet twist rate combo is at or above it you generally have an easier time working with it. What makes most sense is to have a barrel twist rate that will stabilize the heaviest bullet you would want to load at the lowest elevation. Also, realize density altitude is what ballistic calculators use, and that is not always the same at a given geographical position. For example, on a cold, humid morning at 2000 feet elevation the DA could be -800 feet. Later in the day, if high pressure moves in, the temp rises 30 degrees and humidity drops the DA could rise to 3500'. Extreme example for this to happen in the same day, but it will happen from week to week depending on the weather. This weekend on Sunday we had a DA of 2500' at 2000' elevation and Monday was -450 in the same location. I actually do not have experience with a bullet being marginal at low elevation and stable at 6000' higher to answer your specific question, which is a good question, and probably never will as that is a variable that can be eliminated before a single round is fired through the rifle system. That said, I understand what you may be trying to accomplish if the rifle you want to hunt has a slower twist rate than optimal for the bullet you want to load. If I was faced with this scenario I would find a bullet that is stable for this specific gun.</p></blockquote><p></p>
[QUOTE="PNWdude67, post: 1911238, member: 110615"] Work up a load that is stable at the lowest elevation you shoot. The 1.5 stability guideline is just that, and when a bullet twist rate combo is at or above it you generally have an easier time working with it. What makes most sense is to have a barrel twist rate that will stabilize the heaviest bullet you would want to load at the lowest elevation. Also, realize density altitude is what ballistic calculators use, and that is not always the same at a given geographical position. For example, on a cold, humid morning at 2000 feet elevation the DA could be -800 feet. Later in the day, if high pressure moves in, the temp rises 30 degrees and humidity drops the DA could rise to 3500’. Extreme example for this to happen in the same day, but it will happen from week to week depending on the weather. This weekend on Sunday we had a DA of 2500’ at 2000’ elevation and Monday was -450 in the same location. I actually do not have experience with a bullet being marginal at low elevation and stable at 6000’ higher to answer your specific question, which is a good question, and probably never will as that is a variable that can be eliminated before a single round is fired through the rifle system. That said, I understand what you may be trying to accomplish if the rifle you want to hunt has a slower twist rate than optimal for the bullet you want to load. If I was faced with this scenario I would find a bullet that is stable for this specific gun. [/QUOTE]
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