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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Fat bottom gurls....
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<blockquote data-quote="LouBoyd" data-source="post: 518391" data-attributes="member: 9253"><p>Theere are lots of variable which determing what velocity will be most accurate. I don't run my rifles at high pressure, rarely over 90% of SAAMI max for modern rifles and cartridges, but for long range shooting I disagree that slower than close to the practical maximum is usually better. The consistancy which is most important is the grouping at the target, not the extreme spread (ES) or standard deviation (SD) in velocity as mesured with a chronograph. A faster bullet with a larger ES and SD can often produce smaller groups.. Why?</p><p></p><p>Drop is equal to 1/2 g* t^2 where g is the acceleration of gravity ~ 32 ft/sec^2 and T is the time of flight. Given equal bullets the time of flight will always be shorter for the bullet with the higher muzzle velcity if both are stable, making the effect of SD and ES produce smaller vertical stringing. </p><p>Barrel harmonics can increase or decrease the vertical spread at the target of some causes of </p><p>velocity variation. The effect of barrel vibration varies greatly from rifle to rifle. It's difficult enough to predict that ballistic computer programs don't even try, but it's fairly easy to measure with shooting tests. </p><p></p><p>In my opinion the only reliable method of picking a velocity is with ladder tests, shoting a series of shots with slowly increasing loads and seeing where they "bunch", then using a pont near the middle of one bunch as the selected load. The tests shoud be made at the distance the rifle will be used where stringing errors will be most signifcant for achieving desired results. If one bunch has fliers and another doesn't pick the one that doesn't. I've never seen it, but if the bullets in the ladder test just move uniformly up the target with equal spacing I'd still pick the higher velocity end knowing it will have less sensitivity to range estmation errors and lower wind deflection. </p><p></p><p>Measruing ES and ES can show loads which are bound to give bad results, but good ES and SD alone won't guarantee good accuracy. </p><p></p><p>Ladder tests are valid for the conditions they were shot in. They aren't valid if anyitng makes a major change to the velocity of the buillet or which changes the vibrations of the rifle. A large powder temperature change or the additition of a suppressor would be examples. </p><p></p><p>I may scacrifice a couple of hundred fps for better accuracy too, but from my expericnce better accuracy is found at the higher velocity node more often then not when there is more than one practical node to choose from.</p></blockquote><p></p>
[QUOTE="LouBoyd, post: 518391, member: 9253"] Theere are lots of variable which determing what velocity will be most accurate. I don't run my rifles at high pressure, rarely over 90% of SAAMI max for modern rifles and cartridges, but for long range shooting I disagree that slower than close to the practical maximum is usually better. The consistancy which is most important is the grouping at the target, not the extreme spread (ES) or standard deviation (SD) in velocity as mesured with a chronograph. A faster bullet with a larger ES and SD can often produce smaller groups.. Why? Drop is equal to 1/2 g* t^2 where g is the acceleration of gravity ~ 32 ft/sec^2 and T is the time of flight. Given equal bullets the time of flight will always be shorter for the bullet with the higher muzzle velcity if both are stable, making the effect of SD and ES produce smaller vertical stringing. Barrel harmonics can increase or decrease the vertical spread at the target of some causes of velocity variation. The effect of barrel vibration varies greatly from rifle to rifle. It's difficult enough to predict that ballistic computer programs don't even try, but it's fairly easy to measure with shooting tests. In my opinion the only reliable method of picking a velocity is with ladder tests, shoting a series of shots with slowly increasing loads and seeing where they "bunch", then using a pont near the middle of one bunch as the selected load. The tests shoud be made at the distance the rifle will be used where stringing errors will be most signifcant for achieving desired results. If one bunch has fliers and another doesn't pick the one that doesn't. I've never seen it, but if the bullets in the ladder test just move uniformly up the target with equal spacing I'd still pick the higher velocity end knowing it will have less sensitivity to range estmation errors and lower wind deflection. Measruing ES and ES can show loads which are bound to give bad results, but good ES and SD alone won't guarantee good accuracy. Ladder tests are valid for the conditions they were shot in. They aren't valid if anyitng makes a major change to the velocity of the buillet or which changes the vibrations of the rifle. A large powder temperature change or the additition of a suppressor would be examples. I may scacrifice a couple of hundred fps for better accuracy too, but from my expericnce better accuracy is found at the higher velocity node more often then not when there is more than one practical node to choose from. [/QUOTE]
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