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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability: Fine Points to be Aware Of
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<blockquote data-quote="tim_w" data-source="post: 2633793" data-attributes="member: 11132"><p>.........Crap I edited and removed all of my post. Grr</p><p></p><p>.............Ok had most of it saved .</p><p></p><p>Your test is flawed.</p><p></p><p>You shot a bullet at 100 yd in 60F and it grouped well. You then shot the same bullet at the same location in 5F temps @ 500 yd and it key holed.</p><p></p><p>Thos only proves that the same load and bullet in denser air had lower SG. It proves nothing about a bullet having the decreased stability as it travels down range. SG only improves with time downrange.</p><p></p><p></p><p>Further, you did not also shoot the 5F test at 100yd which would have in all likelihood also been keyholing. I assume it was the same load as you were trying to compare apples to apples. Issue is most all gunpowder loses MV as temp drops and certainly going from 60F to 5F. Significant changes when you get well below freezing.</p><p></p><p>For your claim to disprove bullets become less stable downrange you would have had to shoot the same bullet in the same gun/barrel at both 100 yd and then 500 yds. The 100yd would punch round holes small group and the 500 yd target would have oblong or keyholes.</p><p></p><p></p><p>If you were trying to prove the air density increase was the cause, you could have shot at the same location at the same distance. One in warm temps the other in very cold temps but you would need to be doing it over a chrono to show that both loads had the same MV.</p><p></p><p></p><p>BTW all of this has been well proven using very tightly controlled scientific methods. This has been known for a century. In more recent times using doplar radar to track the entire bullet path. Their numerous results conflict directly with your statement that bullets during super sonic flight become less stable over time as the forward velocity decreases. It's been proven that a bullets forward velocity decays at a faster rate than its rotational velocity (rpms).</p><p></p><p>Further you run into the difference in gyroscopic stability and dynamic stability. The latter can be effected by bullet design.</p><p></p><p>Then you have the effects of higher SG on drag model as it traverses flesh. Of the effects on bullet path thru flesh the least effect is gyro stability within the normal range in rifles and bullets. Bullet sectional density and design/construction has far greater effects. </p><p></p><p>If you want to put forward support for your claim that refutes the generally accepted performance by the community then please post up studies or statements from authoritative individuals who conducted tightly controlled studies. Fact is a bullets SG increases over time. This happens because vel decays at a faster rate than rotational decay. Think where the greatest focus of air pressure is on a bullet in flight. It's not on the side of the bullet body with perpendicular focus it's on the tip in a focused cone opposing the direction of flight.</p><p></p><p>This is not touching on bullet design effects o dynamic stability as it crosses into traditional Mach vel such as the mach1.2-0.8 transsonic range. Look at the history of the 30 cal 168 SMK for how a bullet can have plenty of gyroscopic stability SG 1.5+ at MV but because of its design still falls apart as it enters this vel range. Compare it to a Berger 168 gr same SG at MV which will not fall apart as it drops out of solid mach1+ vel.</p><p></p><p> As for subsonic ammo such as the 300 BO/whisper. Most of the MV are in the teansonic range which is the worst window for bullet exit. Mach 0.8-0.9 or 895-1000 fps. Further bullet designed for super sonic flight have differing stability ranges. Bullets designed specifically for subsonic have weight forward designs. If you look at the rpm to vel ratio of a typical super sonic bullet when it reaches subsonic vel it will have a SG far greater and in the range or greater than what's achieved with these faster twist barrels fired at subsonic vel. What it comes down to is bullet design transitional vel windows from Mach 1 to sub vel. You also have the effects of the powders used and the powder volumes are far from ideal for precision. Shoot subsonic in a normal case volune with slower powders and you see a significant improvement in precision. 308 case 220 bullet 850 fps MV 9 tw.</p></blockquote><p></p>
[QUOTE="tim_w, post: 2633793, member: 11132"] .........Crap I edited and removed all of my post. Grr .............Ok had most of it saved . Your test is flawed. You shot a bullet at 100 yd in 60F and it grouped well. You then shot the same bullet at the same location in 5F temps @ 500 yd and it key holed. Thos only proves that the same load and bullet in denser air had lower SG. It proves nothing about a bullet having the decreased stability as it travels down range. SG only improves with time downrange. Further, you did not also shoot the 5F test at 100yd which would have in all likelihood also been keyholing. I assume it was the same load as you were trying to compare apples to apples. Issue is most all gunpowder loses MV as temp drops and certainly going from 60F to 5F. Significant changes when you get well below freezing. For your claim to disprove bullets become less stable downrange you would have had to shoot the same bullet in the same gun/barrel at both 100 yd and then 500 yds. The 100yd would punch round holes small group and the 500 yd target would have oblong or keyholes. If you were trying to prove the air density increase was the cause, you could have shot at the same location at the same distance. One in warm temps the other in very cold temps but you would need to be doing it over a chrono to show that both loads had the same MV. BTW all of this has been well proven using very tightly controlled scientific methods. This has been known for a century. In more recent times using doplar radar to track the entire bullet path. Their numerous results conflict directly with your statement that bullets during super sonic flight become less stable over time as the forward velocity decreases. It's been proven that a bullets forward velocity decays at a faster rate than its rotational velocity (rpms). Further you run into the difference in gyroscopic stability and dynamic stability. The latter can be effected by bullet design. Then you have the effects of higher SG on drag model as it traverses flesh. Of the effects on bullet path thru flesh the least effect is gyro stability within the normal range in rifles and bullets. Bullet sectional density and design/construction has far greater effects. If you want to put forward support for your claim that refutes the generally accepted performance by the community then please post up studies or statements from authoritative individuals who conducted tightly controlled studies. Fact is a bullets SG increases over time. This happens because vel decays at a faster rate than rotational decay. Think where the greatest focus of air pressure is on a bullet in flight. It's not on the side of the bullet body with perpendicular focus it's on the tip in a focused cone opposing the direction of flight. This is not touching on bullet design effects o dynamic stability as it crosses into traditional Mach vel such as the mach1.2-0.8 transsonic range. Look at the history of the 30 cal 168 SMK for how a bullet can have plenty of gyroscopic stability SG 1.5+ at MV but because of its design still falls apart as it enters this vel range. Compare it to a Berger 168 gr same SG at MV which will not fall apart as it drops out of solid mach1+ vel. As for subsonic ammo such as the 300 BO/whisper. Most of the MV are in the teansonic range which is the worst window for bullet exit. Mach 0.8-0.9 or 895-1000 fps. Further bullet designed for super sonic flight have differing stability ranges. Bullets designed specifically for subsonic have weight forward designs. If you look at the rpm to vel ratio of a typical super sonic bullet when it reaches subsonic vel it will have a SG far greater and in the range or greater than what's achieved with these faster twist barrels fired at subsonic vel. What it comes down to is bullet design transitional vel windows from Mach 1 to sub vel. You also have the effects of the powders used and the powder volumes are far from ideal for precision. Shoot subsonic in a normal case volune with slower powders and you see a significant improvement in precision. 308 case 220 bullet 850 fps MV 9 tw. [/QUOTE]
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Stability: Fine Points to be Aware Of
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