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# Time of Flight vs Ballistic Coefficient.

#1
10-28-2006, 02:46 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Time of Flight vs Ballistic Coefficient.

In an effort to free the highjacked thread, I offer this example.

Please note first that the factors that go into wind drift are VERY complex and are not always subject to known mathematical formulas. I say known, because there is a mathematical formula for everything, we just dont always have either the right variables or havent yet figured out how to incorporate certain variables into an equasion. In other words, accurate drift can be always be figured by using math, just not with always with the math we use at this stage in our understanding.

So sometimes, in certain circumstances, a ballistic calculator wont give us a perfect figure, however they can be darn close much of the time. Just for kicks, look at the example below.

Bullet #1: BC of .500 at 3000 FPS at 1K drifts 95.1" with a TOF of 1.5297 sec.

Bullet #2: BC of .400 at 3400 FPS at 1K drifts 110.7" with less of a TOF (1.4933)

Would you say that BC has an effect on wind drift??
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#2
10-28-2006, 02:59 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: Time of Flight vs Ballistic Coefficient.

Also, the calculations in The Reloaders Archive DO NOT use time of flight in any way to calculate wind drift. The calculations are also as accurate as any other program, and in most cases very close if not spot on in real life shooting.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
#3
10-28-2006, 04:31 PM
 Platinum Member Join Date: Jul 2002 Posts: 2,855
Re: Time of Flight vs Ballistic Coefficient.

makes sense to me , the whole math and getting into the theory makes my brain hurt so I just look and watch what the guys winning the comps do , they must be doing somthing right?
Good info , I think that mnore guys should chime in and see what kind of Ideas other folks have on this topic. Its the kinda topic that guys that are new to the Long Range game could learn from or at least clear up alot of misconceptions.
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#4
10-28-2006, 05:31 PM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,088
Re: Time of Flight vs Ballistic Coefficient.

I agree with your first post as to the extremely complicated physics of windage compared to drop and that almost all ballistics are empirical.

As to your second post you probably want to revise it a little. Kinematics is fairly straghtforward and there are ways one can avoid actually writing "t" such as using "x/v", but a person who knows a passing amount of physics can quickly substitute terms and "find" the terms.

Secondly, my two cents, assuming a 10 mph crosswind and a 3000 fps muzzle velocity, what the bullet actually experiences is a vector wind force not two scalars. That vector is {3000fps i + 14.7 fps j}. Consequently, shape is important for wind drift.
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#5
10-28-2006, 10:31 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: Time of Flight vs Ballistic Coefficient.

I am not sure why I should revise my second post. The calculations used in my program dont use TOF. This is a fact.

[ QUOTE ]
Consequently, shape is important for wind drift.

[/ QUOTE ]

I agree.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
#6
10-29-2006, 01:14 AM
 Gold Member Join Date: Sep 2003 Location: Blighty Posts: 637
Re: Time of Flight vs Ballistic Coefficient.

meichele,

I'm not clear why there seems to be an assumption that a bullet's nose-on BC is the only figure to be used when assessing its lateral wind resistance (and therefore the force it will experience from a lateral wind).

If it were possible to make 2 (unspun) bullets of identical nose-on BC but with different cross sectional shapes (for example one a conventional tube and the other with a square cross section such that it presented a vertical flat surface to the wind) why is it assumed that both bullets will be pushed the same amount by a lateral wind? ......despite identical nose-on BC's, I think we would agree that the flat sided bullet would have a greater lateral drag coefficient and consequently be pushed further.

My point is that same calibre bullets are all essentially similar bullet-diameter tubes when side on; and I suspect that their lateral drag coefficients will be very similar (with values certainly far closer than their nose-on values).

So, given that pocket small arms ballistic calculators are basing their calcs on simple algorithms (ie, I don’t think any of them are doing 6 DOF trajectory modelling [img]/ubbthreads/images/graemlins/smile.gif[/img]) I can’t see how the nose-on BC can be taken to have primary relevance

As I said on the other thread...the fact that the small arms ballistic programs that we’re using are indicating drastically different winddrift due to higher nose-on BC is not proof; they give the answers they were written to give!

I don’t doubt that the high nose-on BC bullets will outperform the lower ones…..and, I hope, from the reasoning above you will see that I don’t subscribe to the simple TOF differential theory……….but I cannot see why a nose on BC is being solely used in calculations that actually should involve the bullets lateral drag coefficient ...an algorithm 'fudging' an assumed lateral BC based on, say, the BC of a sideways presented 'standard bullet' (they're all essentially similar bullet-diameter tubes when side on) and the actual bullet's nose on BC as well as the actual wind angle would be more accurate.

……I suspect that (when considering the effects of lateral winds) such programs are treating bullets as spherical point masses. …..and as a result their data outputs are skewed in favour of the high nose-on BC bullets.

...and everyone believes what their computer says [img]/ubbthreads/images/graemlins/smile.gif[/img] a bit like following a GPS into a lake [img]/ubbthreads/images/graemlins/grin.gif[/img]

Will any of this affect the price of fish? No, but I admit that I find it interesting to be forced to think about these things!

I’m away for the next 4 days, but will be keen to read your thoughts on my return ....particularly if you are able to tell me that the current programs do factor lateral drag against wind angle!

All the best

Matt

#7
10-29-2006, 07:04 AM
 Silver Member Join Date: Mar 2006 Location: colo Posts: 124
Re: Time of Flight vs Ballistic Coefficient.

wowzer! what about the bullet going through fog or light rain? [img]/ubbthreads/images/graemlins/wink.gif[/img]
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