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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
300 wm 200 gr Berger hybrid retumbo?? Little advice needed
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<blockquote data-quote="Bart B" data-source="post: 1149849" data-attributes="member: 5302"><p>To me, that means his largest group was probably in the 5 to 6 inch range and the smallest 2 to 3 inches. Quite normal for several 5-shot groups to do that at all ranges.</p><p></p><p>Regarding the 40 fps velocity spread; that bullet has about a 9 inch drop difference. With positive compensation, they'll all strike the same place. With bullets leaving on the muzzle axis up swing, faster ones leave sooner, slower ones leave later. The barrel does not stay still while bullets go through it. It whips and wiggles a lot. The muzzle axis does not point to someplace on the target above the point of aim equal to sight height plus bullet drop until the bullet exits. While aiming, it points somewhere else. Depending on the center of mass of what holds the barreled action (stock, sights, and human) the barrel will whip and wiggle quite a bit at its resonant and harmonic frequencies in some direction until the bullet leaves 1 to 1.5 milliseconds after the round fires.</p><p></p><p>Here's a software page from Border Barrels to show the principals of how that works.</p><p></p><p><a href="http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/barrel_vibrations.htm" target="_blank">Barrel vibrations</a></p><p></p><p>Pick a barrel contour and load, then run the program with 1/10th inch increments of center of mass below the bore axis starting at zero. Note how the bullet leaves at higher angles as the mass center offset increases.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1149849, member: 5302"] To me, that means his largest group was probably in the 5 to 6 inch range and the smallest 2 to 3 inches. Quite normal for several 5-shot groups to do that at all ranges. Regarding the 40 fps velocity spread; that bullet has about a 9 inch drop difference. With positive compensation, they'll all strike the same place. With bullets leaving on the muzzle axis up swing, faster ones leave sooner, slower ones leave later. The barrel does not stay still while bullets go through it. It whips and wiggles a lot. The muzzle axis does not point to someplace on the target above the point of aim equal to sight height plus bullet drop until the bullet exits. While aiming, it points somewhere else. Depending on the center of mass of what holds the barreled action (stock, sights, and human) the barrel will whip and wiggle quite a bit at its resonant and harmonic frequencies in some direction until the bullet leaves 1 to 1.5 milliseconds after the round fires. Here's a software page from Border Barrels to show the principals of how that works. [url=http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/barrel_vibrations.htm]Barrel vibrations[/url] Pick a barrel contour and load, then run the program with 1/10th inch increments of center of mass below the bore axis starting at zero. Note how the bullet leaves at higher angles as the mass center offset increases. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
300 wm 200 gr Berger hybrid retumbo?? Little advice needed
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