[tangolima]

Got home from a trip. Fighting off jet lag and a bug picked up in flight, I finally can get back to this one.

The dope in my previous post was pulled out of my memory. There are a few errors. Let me restate.

Distance 200yd

MV 1250fps

Elevation 26MOA

Zero 50yd (It is a first crossing zero)

Sight height 1.5"

Here are the steps.

The gun's bore inclines above the horizontal line by an launch angle A.

For 50yd zero, A=1.5/50*100=3MOA

For 200yd zero, A = 3 + 26 = 29MOA

A << 6 degree, so principles of flat firing apply. Flight time can be estimated from bullet drop d.

d=29 * 2 = 58" or 4.8'

Actual flight time

tf = sqrt(4.8 * 2 / 32.34) = 547ms

Flight time in vacuum

to = 200*3/1250 = 480ms

10mph wind is equivalent to 14.7fps.

Following point mass model, the wind deflection at 200yd is

w= (0.547 - 0.48)*14.7 = 0.98' or 11.8" or 5.9MOA

A few points to note
1. This method applies to all similar situations, where actual vertical dopes are known. Handy for cast bullets with unknown BC.
2. Flight time is estimated by gravity only. Actually flight time is always longer, although slightly for short distances.
3. Wind deflection (windage dope) is proportional to the cross wind speed. 5.9MOA @10mph, 3MOA @5mph etc.
4. Putting the equation in spreadsheet can be a useful tool.

Hope you find this interesting.

-TL

PS I'm putting together a spreadsheet of this. PM me if you want a copy.

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