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Predicting a Bullet's B.C. ??????

 
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Old 04-22-2006, 05:42 PM
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Join Date: Jun 2002
Location: middle Tennessee
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Predicting a Bullet\'s B.C. ??????

I've been looking at MANY software programs that do lots of things---and even read the threads ABOVE about Ballistic Programs---BUT I haven't found one that can determine the ballistic coefficient of a bullet based on it's dimensions and bullet weight. What about a program that you can design a bullet FIRST and then machine it on a lathe?

Does anyone know what is "THE" ballistic software ("IF" there is a "THE") that can do what I require plus LOTS MORE? PDA downloadable is a plus.

What about the Sierra Infinity 5 program?

THANKS for your comments! [img]/ubbthreads/images/graemlins/blush.gif[/img]
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Old 04-23-2006, 07:31 AM
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Re: Predicting a Bullet\'s B.C. ??????

I'd give Sierra Bullets the nod for having the best stuff around. They've done all their ballistic coefficient work with actual firing tests measuring time of flight. They came up with different BC's for each bullet depending on its speed through the air; some bullets have three or four BC's from the muzzle to target. The BC's they actually measured from other companies were often not nearly what was advertised.

I don't know of any software or book-based stuff that will enable one to design a bullet for a given BC then make them that will actually have that BC when fired. The air flow around the bullet varies with its speed and therefore so does its drag. You may be able to extrapolate a design by averaging shapes from a higher and lower BC bullet for what you want, but finding its actual BC can only be done by measuring its time of flight.
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Old 04-24-2006, 07:58 PM
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Location: The rifle range, or archery range or behind the computer in Alaska
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Re: Predicting a Bullet\'s B.C. ??????

The best way to find a true BC is to go out and do a firing test.

1. You know the velocity

2. You can look up atmospheric data on the web or use a handheld field station.

3. You know the ranges to your targets. 400, 600, 800, 900, 1000 yards.

4. Write down the amount of clicks you had to use to hit dead on from zero. Or Mils, MOA's or whatever method you use to compensate.

5. Go to your software and plug in all the known variables and manipulate the BC until the output matches best.

If you need a place to start, always start with G1 and the manufacturer's published BC. Start at 300 yards (for a 100 yard zero or 400 yards for a 300 yard zero) Go from there.

In the Reloader's Archive, there is a shooting log that converts clicks to inches of drop at range. With that, you then go to the ballistics output page and adjust the BC and drag function until all the numbers match. Once a drag function and BC is set, these stay constant for the purpose of the calculator. From there atmospheric data is changed and the results are displayed.

Some BC calculators can do pretty good, but none will be 100% and even more none will be 80% or better 80% of the time. The best is real world. BC's change from rifle to rifle to so once you find a true BC for a given load, it doesnt mean that it will be the same or even close for that matter in another rifle.

I would say the The Reloader's Archive is "THE" software, but I cant cause I am bias. [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Hope that helps!
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Quote:
Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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