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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).

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For most bullets you can buy, the BC is all you have. What the bullet "sees" (or feels) is the total velocity relative to the air. If you it is going downrange at 3000 f/s and there is a cross wind of 10 mph (call it 15 f/s for the fun of it), the bullet sees a total velocity relative to the wind at a very small angle off the nose (arctan of 15/3000). The wind isn't hitting the side of the bullet.

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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

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The modified point mass does, by using the change in CD (doesn't use BC) for small angles relative to the wind which is what you see for small wind speeds.

This value is of the form: CD0 + alpha^2*CDA2

So as the angle of attack, angle of bullet centerline relative to velocity vector relative to air, increases so does the CD.

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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!

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Or they are just wrong...

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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.**
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I don't know of any that do this. There may be, but the ones that I've seen do the typical aerodynamics formula. The force on the bullet is proportional to the CD and the difference between the velocity and wind vectors. I have the derivation

here.