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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
wind drift based on drag
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<blockquote data-quote="ajhardle" data-source="post: 665521" data-attributes="member: 49861"><p>Right. Reading Bryan's chapter on scaling bullets got my gears in my head rolling. He talks alot about the inherent advantage of scaling up, but neglects the pro's of scaling down. I spend to much time looking at charts and not enough time shooting.</p><p>One thing i noticed, if we scale a bullet down, maintaining form factor and energy ( like going from a .308 to a 6.5-08) the smaller diameter has less drift until the higher b.c. makes up the difference at a range where these bullets are ineffective.</p><p>I started looking into this when bryan states the b.c. advantage of heavy bullets. I thought, at first, the heavier the better, but quickly found out otherwise. the faster the better.</p><p>reveiwing the g7 drag curve, i believe shows why. If the 6.5 leaves the barrel at a velocity of 3156fps, the Cd is something like .26. The .308, with the same energy is slower 2462fps. Cd is close to .284. The difference between the two bullets increase downrange as the slower one reaches the spike in the drag curve. The .308 goes transonic, Cd=.4, and the 6.5 is still happy, close to .3.</p><p>I assumed if i modified the .308's form factor to match the 6.5's Cd at the muzzle, things would even out. Nope. I had to reduce the .308's form factor to .890 to even things at 1000 yards. Comparing form factors of .890 and 1 is no longer apples to apples, or apples to any fruit.</p><p>Am i correct for assuming there is no better way to reduce wind drift than to reduce bullet diameter? That, or get more powder behind it. Same result if my assumptions are correct.</p></blockquote><p></p>
[QUOTE="ajhardle, post: 665521, member: 49861"] Right. Reading Bryan's chapter on scaling bullets got my gears in my head rolling. He talks alot about the inherent advantage of scaling up, but neglects the pro's of scaling down. I spend to much time looking at charts and not enough time shooting. One thing i noticed, if we scale a bullet down, maintaining form factor and energy ( like going from a .308 to a 6.5-08) the smaller diameter has less drift until the higher b.c. makes up the difference at a range where these bullets are ineffective. I started looking into this when bryan states the b.c. advantage of heavy bullets. I thought, at first, the heavier the better, but quickly found out otherwise. the faster the better. reveiwing the g7 drag curve, i believe shows why. If the 6.5 leaves the barrel at a velocity of 3156fps, the Cd is something like .26. The .308, with the same energy is slower 2462fps. Cd is close to .284. The difference between the two bullets increase downrange as the slower one reaches the spike in the drag curve. The .308 goes transonic, Cd=.4, and the 6.5 is still happy, close to .3. I assumed if i modified the .308's form factor to match the 6.5's Cd at the muzzle, things would even out. Nope. I had to reduce the .308's form factor to .890 to even things at 1000 yards. Comparing form factors of .890 and 1 is no longer apples to apples, or apples to any fruit. Am i correct for assuming there is no better way to reduce wind drift than to reduce bullet diameter? That, or get more powder behind it. Same result if my assumptions are correct. [/QUOTE]
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wind drift based on drag
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