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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
calculating bc
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<blockquote data-quote="paphil" data-source="post: 453923" data-attributes="member: 17745"><p>Sometimes things just seem to get too complicated. Someone once said "keep it simple, stupid". I am not too big on math, but I think alot and am somewhat partial to John Porters way of calculating BC. For your initial setup use the data or BC supplied by the manufacturer. These are about all listed in the selection chart with most programs. Shoot your data with the inputs that you have, ie. altitude, temperature, aproxamate muzzle velocity. A chronograph is nice but not a necessity. Most reloading manuels will give something to start with. Now print a chart to use as a guide to figure your real BC and velocity. Set up dead on 0 at 100 or 200 yards. Shoot at 500, 700, and 1000 yards, using the printed chart as a guide. Your gun will probably shoot higher or lower, it doesn't matter , what is important is the data. If you are higher at 1000 than the chart, two things are possible, BC for your bullet is higher or your velocity is higher. Lower than the chart is just the opposite. Now that you know the number of clicks that it takes for your gun at 1000 and are dead on at 200 ,go back to the program and plug in your numbers, floating the velocity. This is very important, at this point we don't want to change the BC. Now print a new chart and it will be dead on at 200 and 1000.( you just put that info in to the chart) Now using your data from 500 and 700, compare them to your new chart. Hopefully they will be very close. If they are both high, your BC is slightly lower and can be tweeked down slightly till your data and that on the chart match. The opposite is done if those two middle numbers are lower than the chart. What we are trying to do is make a chart that matches your data exactly. I never float the BC but always float the velocity.I usually tweek the BC about .010 at a time. If the BC is 620 , I would go to 610 or up to 630. Once you find the matching data you are ready to print the final chart and get your turret printed. That is how I do my guns and scopes and it seems to work very well. The final velocity may vary from the chrono but if the data fits the chart, ballistics don't lie!!</p></blockquote><p></p>
[QUOTE="paphil, post: 453923, member: 17745"] Sometimes things just seem to get too complicated. Someone once said "keep it simple, stupid". I am not too big on math, but I think alot and am somewhat partial to John Porters way of calculating BC. For your initial setup use the data or BC supplied by the manufacturer. These are about all listed in the selection chart with most programs. Shoot your data with the inputs that you have, ie. altitude, temperature, aproxamate muzzle velocity. A chronograph is nice but not a necessity. Most reloading manuels will give something to start with. Now print a chart to use as a guide to figure your real BC and velocity. Set up dead on 0 at 100 or 200 yards. Shoot at 500, 700, and 1000 yards, using the printed chart as a guide. Your gun will probably shoot higher or lower, it doesn't matter , what is important is the data. If you are higher at 1000 than the chart, two things are possible, BC for your bullet is higher or your velocity is higher. Lower than the chart is just the opposite. Now that you know the number of clicks that it takes for your gun at 1000 and are dead on at 200 ,go back to the program and plug in your numbers, floating the velocity. This is very important, at this point we don't want to change the BC. Now print a new chart and it will be dead on at 200 and 1000.( you just put that info in to the chart) Now using your data from 500 and 700, compare them to your new chart. Hopefully they will be very close. If they are both high, your BC is slightly lower and can be tweeked down slightly till your data and that on the chart match. The opposite is done if those two middle numbers are lower than the chart. What we are trying to do is make a chart that matches your data exactly. I never float the BC but always float the velocity.I usually tweek the BC about .010 at a time. If the BC is 620 , I would go to 610 or up to 630. Once you find the matching data you are ready to print the final chart and get your turret printed. That is how I do my guns and scopes and it seems to work very well. The final velocity may vary from the chrono but if the data fits the chart, ballistics don't lie!! [/QUOTE]
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