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Bullet BC

 
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  #1  
Old 04-01-2009, 08:55 PM
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Bullet BC

Is there any way to figure true bullet bc other than with a croney? If so how would I do it and whats the math that goes with?
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  #2  
Old 04-02-2009, 01:09 AM
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Re: Bullet BC

No. You have to know your EXACT velocity to find it.
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  #3  
Old 04-02-2009, 10:51 AM
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Re: Bullet BC

Thanks I guess i will just have to get a croney what model do you recomed? As of right now im shooting a 30-06 and a 204 ruger.
Also in one of the emails you sent me you mentioned G1,G5,G7 drag models is there somewere i could find more info on this subject a book or something?
ps i now i can be really hard headed but i appreciate you patence. I just want to learn as much as a can and have a better understanding!
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  #4  
Old 04-02-2009, 10:00 PM
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Re: Bullet BC

Hey Zach,

Easiest thing I can recommend for you here is to pick up a copy of "Hatcher's Notebook" from Stackpole press. There are a complete set of drag tables, along with several examples of how they're used. You still need to know velocity at two different points, and that's absolutely required to calculate a BC. The tables in the book are Ingalls', which can be used almost interchangeably with the G1 currently in use for US sporting bullets and ammunition. There's also an abbreviated copy of the Coxe-Bugless charts for estimating ogive values and ballistic coefficients by this shape. Not very precise, but an interesting history lesson today. It's worth picking up a copy of Hatcher's Notebook anyway, and every serious shooter should have a copy on his bench.

If you really want to get serious here, there's "Modern Exterior Ballistics" by the late Bob McCoy. It's available from Schiffer publishing, but it's a bit steep at close to $100 a copy. It will still require the same basic info here; known velocities from two different points downrange. Anything beyond this, such as methods based on shape, basically comes down to an "educated guesstimate."

Hope this helps,

Kevin Thomas
Berer Bullets
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  #5  
Old 04-02-2009, 10:14 PM
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Re: Bullet BC

Quote:
Originally Posted by Kevin Thomas View Post
Hey Zach,

Easiest thing I can recommend for you here is to pick up a copy of "Hatcher's Notebook" from Stackpole press. There are a complete set of drag tables, along with several examples of how they're used. You still need to know velocity at two different points, and that's absolutely required to calculate a BC. The tables in the book are Ingalls', which can be used almost interchangeably with the G1 currently in use for US sporting bullets and ammunition. There's also an abbreviated copy of the Coxe-Bugless charts for estimating ogive values and ballistic coefficients by this shape. Not very precise, but an interesting history lesson today. It's worth picking up a copy of Hatcher's Notebook anyway, and every serious shooter should have a copy on his bench.

If you really want to get serious here, there's "Modern Exterior Ballistics" by the late Bob McCoy. It's available from Schiffer publishing, but it's a bit steep at close to $100 a copy. It will still require the same basic info here; known velocities from two different points downrange. Anything beyond this, such as methods based on shape, basically comes down to an "educated guesstimate."

Hope this helps,


Kevin Thomas
Berer Bullets
Wow that is steep! is there a certian croney or set of croneys that would be good. Also could i use one croney set it up at the muzzle for say 20 shots then move the croney to the target and take 20 shots then take averege's for each to get a true bullet bc?
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  #6  
Old 04-02-2009, 10:38 PM
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Re: Bullet BC

Hi Zach,

Well, you could do that, but frankly, the results are going to be a highly suspect educated guess, nothing more. There's a lot of factors that come into play here, and chrono errors are always a part of that. This is mostly due to their set-up, screen separation distances, distance to muzzle, etc.. Add to this the errors induced by trying to reset the same screens at a different distance, firing another set of the "same" ammunition, and basically you've got a recipe for a real goat rope here. Not worth the time or effort to wind up with what would be very suspect (at best) data. The easiest way here would be to use something like the Oehler 43, which is capable of generating BCs and is a more or less self contained unit. Rather than do all this, I'd really suggest you pick up that copy of Hatcher's Notebook. It will explain a lot of this in pretty readable terms, and there's a wealth of other information in there as well. I think I've gone through about four copies over the years and read the covers off them, quite literally.

Kevin
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  #7  
Old 04-02-2009, 10:57 PM
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Re: Bullet BC

Ok thanks ill look that up!
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