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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Let's argue about BC's
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<blockquote data-quote="paphil" data-source="post: 475518" data-attributes="member: 17745"><p>What is the reason for knowing the exact BC ? When we use the BC and chronographed velocities to attempt to produce an accurate drop chart, we setting ourselves up for grief ! Manufactures BC's are nice and help us to get "on the paper" but don't address the variations of each gun. I just spent ten days at the eastern sports show trying to explain how to set up scopes for Best of the West and it seems that most shooters want an accurate drop chart but have bought the idea of the generic turret as being good enough. To get an extreamly accurate drop chart, several steps are necessary. </p><p>I use the program at the BOTW website with it's hugh list of bullets and BCs. Find your bullet and BC and begin entering your data. Scope height, click value, tempature, elevation, ect. Calculate to get a starting point and print out the chart to have as a range card.Now go shoot your data. I shoot in dead on at 200 and use the chart to find an on paper hold for 500 and 1000. The chart might suggest 64 clicks at 1000 and my gun might take 68 or 60. Write down your results. Do the same at 500 and as many other distances as you care to shoot. What we are doing is defining an arc for your bullet. Take these results back to the computer program and plug in the far target information and float the velocity (BC must remain constant). Now calculate. The new chart will list your drop as exactly correct for 1000 yards. Now compare your info for the mid ranges with the new chart values. If the 500 yard value is higher or lower than your data value , bump the program BC up or down a few points and recalculate until your data matches . The BC now matches your bullet and the drop chart can be printed and used to make a custom turret. I don't know of any other way to get true BC and even though the chronograph and the mfg BC don't exactly match my chart, my bullets flight path does match. Also with this info I can change inputs for temp and altitude to produce charts for any hunt I'm going on.</p></blockquote><p></p>
[QUOTE="paphil, post: 475518, member: 17745"] What is the reason for knowing the exact BC ? When we use the BC and chronographed velocities to attempt to produce an accurate drop chart, we setting ourselves up for grief ! Manufactures BC's are nice and help us to get "on the paper" but don't address the variations of each gun. I just spent ten days at the eastern sports show trying to explain how to set up scopes for Best of the West and it seems that most shooters want an accurate drop chart but have bought the idea of the generic turret as being good enough. To get an extreamly accurate drop chart, several steps are necessary. I use the program at the BOTW website with it's hugh list of bullets and BCs. Find your bullet and BC and begin entering your data. Scope height, click value, tempature, elevation, ect. Calculate to get a starting point and print out the chart to have as a range card.Now go shoot your data. I shoot in dead on at 200 and use the chart to find an on paper hold for 500 and 1000. The chart might suggest 64 clicks at 1000 and my gun might take 68 or 60. Write down your results. Do the same at 500 and as many other distances as you care to shoot. What we are doing is defining an arc for your bullet. Take these results back to the computer program and plug in the far target information and float the velocity (BC must remain constant). Now calculate. The new chart will list your drop as exactly correct for 1000 yards. Now compare your info for the mid ranges with the new chart values. If the 500 yard value is higher or lower than your data value , bump the program BC up or down a few points and recalculate until your data matches . The BC now matches your bullet and the drop chart can be printed and used to make a custom turret. I don't know of any other way to get true BC and even though the chronograph and the mfg BC don't exactly match my chart, my bullets flight path does match. Also with this info I can change inputs for temp and altitude to produce charts for any hunt I'm going on. [/QUOTE]
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