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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet stability
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<blockquote data-quote="RockyMtnMT" data-source="post: 1335838" data-attributes="member: 7999"><p>It was pointed out to me that bullets become more stable as they slow down. It appears that this is indeed true. I can not find out how much stability increases relative to the velocity of the bullet though. The Hornady calculator show huge increases in stability as the bullet slows down in flight. This does not make sense to me for a couple of reasons. It does not line up with range test results and it does not make sense with the findings of Litz showing the need for a min of 1.5sg for optimal bc. The Hornady calculator shows a 1.4sg bullet becoming higher than 1.5sg inside of 100y of slowing down and over 5.0 at 1500y. So if the Hornady data is correct the 1.5sg minimum would be of very little factor at long range as related to bc.</p><p></p><p>Turns out that there is also dynamic stability (sd) to go along with gyroscopic stability (sg). So far what I have found is that sd may be the larger contributor to unstable bullet performance down range. I think this has something to do with why we see the same bullet give different results from one rifle to the next for the bc value that lines up with the drops.</p><p></p><p>Just when I thought I had a grip on stability now I need to learn about sd and what makes it good or bad.</p><p></p><p>We have done a lot of testing on bullets and their terminal performance relative to sg. Our results have shown that bullets that are below a 1.5sg will have trouble giving satisfactory terminal performance. From our testing a bullet should have at minimum a 1.5sg for hunting. The faster the rotational spin of a bullet is the longer it stays point oriented after contact, resulting in bullets performing as they are designed. Less than 1.5sg increases the chance of bullets failing to expand. We do our testing at short range for the convenience of it, but I have witnessed marginal stability resulting in poor terminal performance on animals, but according to the Hornady model that bullet would have been well over 1.5sg by the time it impacted the animal. </p><p></p><p>At this point I am going to stick with what I have seen with test results and the need for 1.5sg at the muzzle for good flight ballistics and terminal performance. In fact this year I am changing to lighter bullets with higher sg for hunting and adjusting my max range accordingly to ensure better terminal performance. I have made the decision that better terminal performance out weighs the extended range of the higher bc bullets that are not as high for sg.</p><p></p><p>Steve</p></blockquote><p></p>
[QUOTE="RockyMtnMT, post: 1335838, member: 7999"] It was pointed out to me that bullets become more stable as they slow down. It appears that this is indeed true. I can not find out how much stability increases relative to the velocity of the bullet though. The Hornady calculator show huge increases in stability as the bullet slows down in flight. This does not make sense to me for a couple of reasons. It does not line up with range test results and it does not make sense with the findings of Litz showing the need for a min of 1.5sg for optimal bc. The Hornady calculator shows a 1.4sg bullet becoming higher than 1.5sg inside of 100y of slowing down and over 5.0 at 1500y. So if the Hornady data is correct the 1.5sg minimum would be of very little factor at long range as related to bc. Turns out that there is also dynamic stability (sd) to go along with gyroscopic stability (sg). So far what I have found is that sd may be the larger contributor to unstable bullet performance down range. I think this has something to do with why we see the same bullet give different results from one rifle to the next for the bc value that lines up with the drops. Just when I thought I had a grip on stability now I need to learn about sd and what makes it good or bad. We have done a lot of testing on bullets and their terminal performance relative to sg. Our results have shown that bullets that are below a 1.5sg will have trouble giving satisfactory terminal performance. From our testing a bullet should have at minimum a 1.5sg for hunting. The faster the rotational spin of a bullet is the longer it stays point oriented after contact, resulting in bullets performing as they are designed. Less than 1.5sg increases the chance of bullets failing to expand. We do our testing at short range for the convenience of it, but I have witnessed marginal stability resulting in poor terminal performance on animals, but according to the Hornady model that bullet would have been well over 1.5sg by the time it impacted the animal. At this point I am going to stick with what I have seen with test results and the need for 1.5sg at the muzzle for good flight ballistics and terminal performance. In fact this year I am changing to lighter bullets with higher sg for hunting and adjusting my max range accordingly to ensure better terminal performance. I have made the decision that better terminal performance out weighs the extended range of the higher bc bullets that are not as high for sg. Steve [/QUOTE]
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