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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Computerized Ballistic Solutions
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<blockquote data-quote="Blaine Fields" data-source="post: 29041" data-attributes="member: 183"><p>Jeff,</p><p></p><p>There is no single drag function that will describe a bullet's velocity from muzzle to zero fps. If you look at the graph above you will see essentially four distinct zones. Supersonic (curvalinear, above 1400 fps); transonic (flat and linear, 1200 to 1400 fps); subsonic (linear, 1200 - 900 fps), and the zero to 900 fps region which is basically flat and linear. Because three of the zones are essentially linear, describing them is not difficult. It is the curvalinear portion at 1400 fps and above that is the problem.</p><p></p><p>But it turns out that the major practical differences between spire-point, flat based bullets and VLD types has more to do with the <em>rate</em> of deceleration between the two as opposed to the underlying mathematical drag function. So, as Pejsa has shown, it is possible to use a G1 scaling factor together with a uniform drag function as long as the user can also vary the rate of deceleration from bullet type to bullet type. In other words, the shooter must be able to correlate a bullet with a deceleration constant. </p><p></p><p>I'll tell you what: take your program and input: atm. pressure @ 29.85, temp @ 75, humidity @ 78%, 190 gr. .30 cal. bullet (Berger VLD) with a BC (G1) of 0.583 and muzzle velocity of 2900 fps. My program forcasts an elevation correction of 29.5 MOA for a 1000 yd shot. It is right on in real life. I know because I have shot that bullet under these precise conditions and I am dead-spanking-on.</p><p></p><p>What does your program forecast using the G1 or G7? If it ain't 29.5 MOA, it ain't right. The Horus program I have (the Atrag2P, ver 2.40) predicts 27.6 MOA. It is not even close to real world.</p><p></p><p>[ 10-27-2003: Message edited by: Blaine Fields ]</p></blockquote><p></p>
[QUOTE="Blaine Fields, post: 29041, member: 183"] Jeff, There is no single drag function that will describe a bullet's velocity from muzzle to zero fps. If you look at the graph above you will see essentially four distinct zones. Supersonic (curvalinear, above 1400 fps); transonic (flat and linear, 1200 to 1400 fps); subsonic (linear, 1200 - 900 fps), and the zero to 900 fps region which is basically flat and linear. Because three of the zones are essentially linear, describing them is not difficult. It is the curvalinear portion at 1400 fps and above that is the problem. But it turns out that the major practical differences between spire-point, flat based bullets and VLD types has more to do with the [I]rate[/I] of deceleration between the two as opposed to the underlying mathematical drag function. So, as Pejsa has shown, it is possible to use a G1 scaling factor together with a uniform drag function as long as the user can also vary the rate of deceleration from bullet type to bullet type. In other words, the shooter must be able to correlate a bullet with a deceleration constant. I'll tell you what: take your program and input: atm. pressure @ 29.85, temp @ 75, humidity @ 78%, 190 gr. .30 cal. bullet (Berger VLD) with a BC (G1) of 0.583 and muzzle velocity of 2900 fps. My program forcasts an elevation correction of 29.5 MOA for a 1000 yd shot. It is right on in real life. I know because I have shot that bullet under these precise conditions and I am dead-spanking-on. What does your program forecast using the G1 or G7? If it ain't 29.5 MOA, it ain't right. The Horus program I have (the Atrag2P, ver 2.40) predicts 27.6 MOA. It is not even close to real world. [ 10-27-2003: Message edited by: Blaine Fields ] [/QUOTE]
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