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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Shootings biggest Misconception!!
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<blockquote data-quote="Bart B" data-source="post: 1156920" data-attributes="member: 5302"><p>'Twas either the US Army or USMC rifle team that testing M14NM's in accuracy cradles, they shot smaller test groups in MOA at 600 yards than at 300 with the same ammo; not much, but easily seen. The Brit's proved a century ago that some barrels positively compensate for bullet velocity making long range groups smaller than those at shorter ranges; no wonder they shot better scores at long range than our M1903's with less .30-06 velocity spread than the .303 rounds:</p><p></p><p><a href="https://archive.org/details/philtrans05900167" target="_blank">https://archive.org/details/philtrans05900167</a></p><p></p><p>Tuners have been used for some time to tune the barrel's resonant and harmonic frequencies so it points at the best place to compensate for muzzle velocity spreads; higher angles for slower bullets, vice versa for faster ones leaving at a lower angle. Happens when barrel muzzle axis is on the up swing. One shown in the below link and there's others listed on Varmint Al's site: </p><p></p><p><a href="http://www.varmintal.net/aeste.htm" target="_blank">Barrel Tuner Analysis -- FEA Dynamic Analysis of Esten's Rifle with/without a Tuner.</a></p><p></p><p>All bullets don't leave at the same speed. Slower ones will drop further down range that faster ones. A 50 fps spread in .308 Win ammo shows a 1/10th MOA vertical spread at 100 yards; at 1000, it's 2 MOA. According to decent ballistic software.</p><p></p><p>All bullets leaving at the same speed do not have the same BC. As some bullets are more unbalanced than others, they'll have lower BC numbers than the others. That means more vertical stringing.</p><p></p><p>All bullets do not leave the muzzle at the same angle relative to the line of sight. Barrel times have a small spread even when they leave at the same speed. Pressure curves are not repeatable and vary a tiny bit. How much the barrel whips and the direction it whips at is determined by where the bore axis is aligned relative to the center of mass holding the rifle. The further away it is, the more it'll whip before the bullet leaves and that changes the angle it leaves at relative to the line of sight it was fired in. (This is the reason different people have different zeros for the same rifle and ammo.)</p><p></p><p>Benchrest records through 300 yards show each 100 yards past the first one have aggregate groups larger in MOA; about .2 at 100, .27 at 300 and .35 at 300.</p><p></p><p>Subtle atmospheric conditions that are not stable causes bullets to move around in flight even if they leave at the same speed at the same angle and all are perfectly balanced. The further down range the bullet is, the more a given air movement/density changes, so will that change its trajectory</p><p></p><p>Therefore. . .</p><p></p><p>'Tis my opinion that all groups down range increase in MOA sizes. No way does a bullet leaving at the same angle and direction form LOS at some point at the edge of a short range aerial group know what direction to change its path then head back towards center for a group further down range. Positive compensation for barrel whip excluded.</p><p></p><p>To me, 'twould be interesting to see muzzle velocity numbers for each shot in Brian's tests through 300 yards.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1156920, member: 5302"] 'Twas either the US Army or USMC rifle team that testing M14NM's in accuracy cradles, they shot smaller test groups in MOA at 600 yards than at 300 with the same ammo; not much, but easily seen. The Brit's proved a century ago that some barrels positively compensate for bullet velocity making long range groups smaller than those at shorter ranges; no wonder they shot better scores at long range than our M1903's with less .30-06 velocity spread than the .303 rounds: [url]https://archive.org/details/philtrans05900167[/url] Tuners have been used for some time to tune the barrel's resonant and harmonic frequencies so it points at the best place to compensate for muzzle velocity spreads; higher angles for slower bullets, vice versa for faster ones leaving at a lower angle. Happens when barrel muzzle axis is on the up swing. One shown in the below link and there's others listed on Varmint Al's site: [url=http://www.varmintal.net/aeste.htm]Barrel Tuner Analysis -- FEA Dynamic Analysis of Esten's Rifle with/without a Tuner.[/url] All bullets don't leave at the same speed. Slower ones will drop further down range that faster ones. A 50 fps spread in .308 Win ammo shows a 1/10th MOA vertical spread at 100 yards; at 1000, it's 2 MOA. According to decent ballistic software. All bullets leaving at the same speed do not have the same BC. As some bullets are more unbalanced than others, they'll have lower BC numbers than the others. That means more vertical stringing. All bullets do not leave the muzzle at the same angle relative to the line of sight. Barrel times have a small spread even when they leave at the same speed. Pressure curves are not repeatable and vary a tiny bit. How much the barrel whips and the direction it whips at is determined by where the bore axis is aligned relative to the center of mass holding the rifle. The further away it is, the more it'll whip before the bullet leaves and that changes the angle it leaves at relative to the line of sight it was fired in. (This is the reason different people have different zeros for the same rifle and ammo.) Benchrest records through 300 yards show each 100 yards past the first one have aggregate groups larger in MOA; about .2 at 100, .27 at 300 and .35 at 300. Subtle atmospheric conditions that are not stable causes bullets to move around in flight even if they leave at the same speed at the same angle and all are perfectly balanced. The further down range the bullet is, the more a given air movement/density changes, so will that change its trajectory Therefore. . . 'Tis my opinion that all groups down range increase in MOA sizes. No way does a bullet leaving at the same angle and direction form LOS at some point at the edge of a short range aerial group know what direction to change its path then head back towards center for a group further down range. Positive compensation for barrel whip excluded. To me, 'twould be interesting to see muzzle velocity numbers for each shot in Brian's tests through 300 yards. [/QUOTE]
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Shootings biggest Misconception!!
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