Can someone give me a place to look for the equations necessary to calculate a theoretical Ballistic Coefficient? I'm kicking around an idea in my head and I'd like to put some theory up against it but I don't have the equations for a BC.
Range Report Calculating Theoretical BC
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Re: Calculating Theoretical BC
http://www.eskimo.com/~jbm/cgi-bin/jbmbcv-5.0.cgi
near fps far fps drop of fps over distance gives BC
http://www.eskimo.com/~jbm/cgi-bin/jbmbcv-5.0.cgi
near fps far fps drop of fps over distance gives BC
Re: Calculating Theoretical BC
+1 on JBM.... in my opinion its all theory until you shoot it on paper out to 1k and get the right data
+1 on JBM.... in my opinion its all theory until you shoot it on paper out to 1k and get the right data
Re: Calculating Theoretical BC
Is this what you are looking for?
http://en.wikipedia.org/wiki/Ballistic_coefficient
Is this what you are looking for?
http://en.wikipedia.org/wiki/Ballistic_coefficient
Re: Calculating Theoretical BC
He asked for the *formulae*, not for a website that automagically calculates it for him.
One site that has a <span style="font-style: italic">lot</span> of good information is http://exteriorballistics.com - hosted, I believe, by Sierra Bullets, as it has most of the good content from their older manuals before ballistic programs started doing all the grunt work for us. Specifically, the document 'The Ballistic Coefficient' goes over what BC is and isn't and some discussion of how to calculate it. Also the online section 4 of the 4th Ed. loading manual has some good info in it as well. Not much in the way of worked examples, though. The sections from the 5th edition manual show some pretty good explanations - though most of the material is slanted towards justifying their use of velocity-banded G1 BC models, FWIW.
He asked for the *formulae*, not for a website that automagically calculates it for him.
One site that has a <span style="font-style: italic">lot</span> of good information is http://exteriorballistics.com - hosted, I believe, by Sierra Bullets, as it has most of the good content from their older manuals before ballistic programs started doing all the grunt work for us. Specifically, the document 'The Ballistic Coefficient' goes over what BC is and isn't and some discussion of how to calculate it. Also the online section 4 of the 4th Ed. loading manual has some good info in it as well. Not much in the way of worked examples, though. The sections from the 5th edition manual show some pretty good explanations - though most of the material is slanted towards justifying their use of velocity-banded G1 BC models, FWIW.
Re: Calculating Theoretical BC
I'm looking for the theory because I'm not going to have dies made for a profile that sucks. I can take a known profile with a known real world BC, calculate it's theoretical BC and then calculate the theoretical BC for the bullet profile.
I need something to give me an idea of whether or not I'm wasting time and money making bullet forming dies for something that's not any better than buying an already existing bullet.
The Wiki page helps some, but it only gives the G1 coefficient and I don't know how to calculate the Cd either.
I did see the comparison page on JBM that translates a G1 into a G7 so that will get me the G7 that I'm looking for.
Thanks for the info Memilanuk, those pages are what I was looking for.
I'm looking for the theory because I'm not going to have dies made for a profile that sucks. I can take a known profile with a known real world BC, calculate it's theoretical BC and then calculate the theoretical BC for the bullet profile.
I need something to give me an idea of whether or not I'm wasting time and money making bullet forming dies for something that's not any better than buying an already existing bullet.
The Wiki page helps some, but it only gives the G1 coefficient and I don't know how to calculate the Cd either.
I did see the comparison page on JBM that translates a G1 into a G7 so that will get me the G7 that I'm looking for.
Thanks for the info Memilanuk, those pages are what I was looking for.
Re: Calculating Theoretical BC
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">I'm looking for the theory because I'm not going to have dies made for a profile that sucks. I can take a known profile with a known real world BC, calculate it's theoretical BC and then calculate the theoretical BC for the bullet profile.
I need something to give me an idea of whether or not I'm wasting time and money making bullet forming dies for something that's not any better than buying an already existing bullet.
I did see the comparison page on JBM that translates a G1 into a G7 so that will get me the G7 that I'm looking for.
</div></div>
Bohem,
I’m not really sure how to respond to this one but my gut saying you’re going about this wrong way.
I’m sure what you want to have built has been built before or something very close to it. Knowing a theoretical BC of a bullet is really going to accomplish what in the big picture??? There’s so much more to exterior ballistics than knowing the published G1 ballistic coefficient which to me is totally useless.
Depending on the bullet type you’re shooting there’s a G5, G6, G7, G8 CD (coefficient drag) models to name a few. G7 isn’t a one size fits all CD model.
My advice and its only advice is to poll this board and a few others with the caliber, bullet type and weight you’re looking to build. Ask about accuracy, typical velocity readings, throat erosion and barrel life expectancy.
Knowing a bullets BC and/or corrected CD model or how to calculate them is only going to you that. In theory it doesn’t tell you anything that isn’t already published or how well it’s going to perform.
Still scratching my head on your logic? Let us help if we can.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">I'm looking for the theory because I'm not going to have dies made for a profile that sucks. I can take a known profile with a known real world BC, calculate it's theoretical BC and then calculate the theoretical BC for the bullet profile.
I need something to give me an idea of whether or not I'm wasting time and money making bullet forming dies for something that's not any better than buying an already existing bullet.
I did see the comparison page on JBM that translates a G1 into a G7 so that will get me the G7 that I'm looking for.
</div></div>
Bohem,
I’m not really sure how to respond to this one but my gut saying you’re going about this wrong way.
I’m sure what you want to have built has been built before or something very close to it. Knowing a theoretical BC of a bullet is really going to accomplish what in the big picture??? There’s so much more to exterior ballistics than knowing the published G1 ballistic coefficient which to me is totally useless.
Depending on the bullet type you’re shooting there’s a G5, G6, G7, G8 CD (coefficient drag) models to name a few. G7 isn’t a one size fits all CD model.
My advice and its only advice is to poll this board and a few others with the caliber, bullet type and weight you’re looking to build. Ask about accuracy, typical velocity readings, throat erosion and barrel life expectancy.
Knowing a bullets BC and/or corrected CD model or how to calculate them is only going to you that. In theory it doesn’t tell you anything that isn’t already published or how well it’s going to perform.
Still scratching my head on your logic? Let us help if we can.
Re: Calculating Theoretical BC
Jeff-
The VLD bullets, Amax and SMK's (I think the SMK) are all a Secant ogive. Some bullets are Tangent Ogive.
There's something called a von Karmann -Trefts ogive.
It's somewhat of a bastard to cut the profile because it doesn't correspond to any geometric things like "partial filet here, radius of this here, profile here" like a secant or a tangent ogive can give you. The general consensus when talking to a couple of supersonic aerodynamics people I know from work was that it would be great but the ability to make the dies are probably slim. That's where another friend comes in, if it's a viable on paper he's willing to spark up the CNC to profile it for me.
The vKT ogive profile is calculated only by a purely mathematical function. I want to compare the theoretical results from something already known to perform. Use this kind of comparison to get a baseline for the empirical comparison between theory to practice for the G1, G5, G6, G7, G8 etc. so that I get at least an idea if it's something that might be worth trying to make a few of.
If the calculated theoretical results for the vKT ogive are not reasonably improved over a Secant Ogive then it's not worth the run of machinery to prove that.
Sometimes I don't mind polling information like that, but this isn't a caliber specific thing, unless someone else did the calculations already and wants to discuss what they found, a poll won't solve the problem. I also avoided the polls because I didn't feel like having a pointless thread full of "180 Berger in 7mm WSM FTW". Just like the 2 replies above that said "until you shoot it to 1k it's just a waste of time" there's nothing really informative there. That's akin to saying "don't do any calculations, just go build the airplane and set it down the runway, if it doesn't crash we're good."
I would really like to discuss the theory behind it and help understand myself what goes into the flight mechanics. Having to work through the calculations and work up information that doesn't yet exist is part of the learning experience.
I don't mean any of this to come off as a smart-ass remark to you, I understand you're just asking questions to understand and I should clarify it more. Thanks.
Jeff-
The VLD bullets, Amax and SMK's (I think the SMK) are all a Secant ogive. Some bullets are Tangent Ogive.
There's something called a von Karmann -Trefts ogive.
It's somewhat of a bastard to cut the profile because it doesn't correspond to any geometric things like "partial filet here, radius of this here, profile here" like a secant or a tangent ogive can give you. The general consensus when talking to a couple of supersonic aerodynamics people I know from work was that it would be great but the ability to make the dies are probably slim. That's where another friend comes in, if it's a viable on paper he's willing to spark up the CNC to profile it for me.
The vKT ogive profile is calculated only by a purely mathematical function. I want to compare the theoretical results from something already known to perform. Use this kind of comparison to get a baseline for the empirical comparison between theory to practice for the G1, G5, G6, G7, G8 etc. so that I get at least an idea if it's something that might be worth trying to make a few of.
If the calculated theoretical results for the vKT ogive are not reasonably improved over a Secant Ogive then it's not worth the run of machinery to prove that.
Sometimes I don't mind polling information like that, but this isn't a caliber specific thing, unless someone else did the calculations already and wants to discuss what they found, a poll won't solve the problem. I also avoided the polls because I didn't feel like having a pointless thread full of "180 Berger in 7mm WSM FTW". Just like the 2 replies above that said "until you shoot it to 1k it's just a waste of time" there's nothing really informative there. That's akin to saying "don't do any calculations, just go build the airplane and set it down the runway, if it doesn't crash we're good."
I would really like to discuss the theory behind it and help understand myself what goes into the flight mechanics. Having to work through the calculations and work up information that doesn't yet exist is part of the learning experience.
I don't mean any of this to come off as a smart-ass remark to you, I understand you're just asking questions to understand and I should clarify it more. Thanks.
Re: Calculating Theoretical BC
Ok give this a try copy and paste from Lindy's post on similar discussion.
Modern Exterior Ballistics by Robert McCoy is probably the classic work on that subject. You'll find lots there to keep you entertained.
http://www.amazon.com/Modern-Exterior-Ballistics-Symmetric-Projectiles/dp/0764307207
If you buy the book, there is a nice file you may like with some correction to the original here:
http://www.dexadine.com/download/mccoy04.pdf
Ok give this a try copy and paste from Lindy's post on similar discussion.
Modern Exterior Ballistics by Robert McCoy is probably the classic work on that subject. You'll find lots there to keep you entertained.
http://www.amazon.com/Modern-Exterior-Ballistics-Symmetric-Projectiles/dp/0764307207
If you buy the book, there is a nice file you may like with some correction to the original here:
http://www.dexadine.com/download/mccoy04.pdf
Re: Calculating Theoretical BC
Thanks, I'll read through there too. If/When I get to actually coming up with numbers I'll let you guys know. I'm sure I'll be back to ask more questions.
Thanks, I'll read through there too. If/When I get to actually coming up with numbers I'll let you guys know. I'm sure I'll be back to ask more questions.
Re: Calculating Theoretical BC
RSI Shooting lab software will do it. You can put in the bullet specs i.e. boat tail lenth, boat tail diamiter, nose length, tip diamiter, oal, ect. and it will figure out the bc for you in G1,G5,G7 plus 4 others.
Give it a look.
www.shootingsoftware.com
Scott
RSI Shooting lab software will do it. You can put in the bullet specs i.e. boat tail lenth, boat tail diamiter, nose length, tip diamiter, oal, ect. and it will figure out the bc for you in G1,G5,G7 plus 4 others.
Give it a look.
www.shootingsoftware.com
Scott
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