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# Wind shooting

#8
02-17-2004, 09:32 AM
 Silver Member Join Date: Dec 2003 Location: Stamford NY Posts: 160
Re: Wind shooting

Dave,

That answer makes alot of sense, but im going to also ask would that only work if the bullet was moving at a constant speed, by the time the bullet gets out there its moveing alot slower and the wind has more time to act on it causing more than 1/2moa drift [img]images/icons/confused.gif[/img].
#9
02-17-2004, 10:47 AM
 Silver Member Join Date: Jan 2004 Location: New Mexico Posts: 113
Re: Wind shooting

I don't really think it has all that much more time. There are really two things we're talking about here. First, how much angular deflection you get for a given wind and second, how much that angular deflection moves the bullet. Of course if the deflection is farther down range then it causes less wind drift on the target.

I've never been good at remembering numbers so I ran a few of test cases with a point mass program. They are all 10 mile/hour winds. One is a constant wind from 0 to 1000 yards. The next is from 0 to 100 yards and the third is 500 to 600 yards. All have trajectories to 1000 yards.

Here are the URLs:

wind_10_000_1000.txt
wind_10_000_100.txt
wind_10_500_600.txt

Please note the version number of the program running these (&lt;1) so I'm covering my butt.
__________________
JBM Small Arms Ballistics -- http://www.eskimo.com/~jbm
#10
02-17-2004, 10:59 AM
 Silver Member Join Date: Jan 2004 Location: New Mexico Posts: 113
Re: Wind shooting

Also I might add that the deflection at the near range (0 to 100 yards) is about .6 inches and at the 500-600 yard range is about an inch. The difference at 1000 yards ends up being a few inches.

Here's another file with the same 10 mile an hour wind from 900 to 1000 yards.

wind_10_900_1000.txt

Note that the deflection is at little more than twice (1.5") about the 0 to 100 yard wind deflection which is what we would expect since the velocity has fallen to less than half the muzzle velocity. (See the standard wind formula and you'll see that it has the velocity in the denominator...)
__________________
JBM Small Arms Ballistics -- http://www.eskimo.com/~jbm
#11
02-17-2004, 11:12 AM
 Platinum Member Join Date: May 2001 Posts: 2,377
Re: Wind shooting

JBM

Thanks for the reply and most welcome info. This is the first time I've seen this type of output from a ballistics program and I'm excited.

Would you be so kind as to rerun this same info with a muzzle velocity of 2660, BC of .470 @ STP. This I believe is about the standard for the "older" standard military "sniper" rounds data that I've somewhat committed to memory.

Thanks.
#12
02-17-2004, 11:22 AM
 Silver Member Join Date: Dec 2003 Location: Stamford NY Posts: 160
Re: Wind shooting

JBM,

Thanks for posting that, I looks that wind effect the bullet at the same angle thru out its trajectory, it just depends on where the wind start/stops inorder to determine the amount of drift.

Thanks,
Brian
#13
02-17-2004, 11:39 AM
 Platinum Member Join Date: May 2001 Posts: 2,377
Re: Wind shooting

Brian

That's what I read from JBM's posts and have understood to some degree. Constant wind over the entire flight is additive to previous wind caused deflection. Singlular (short wind period(s)) are more difficult but there is no more cumulative induced deflection after the initial deflection, just continuation of the angular error. Confused myself on that one!

[ 02-17-2004: Message edited by: Dave King ]
#14
02-17-2004, 01:00 PM
 Silver Member Join Date: Jan 2004 Location: New Mexico Posts: 113
Re: Wind shooting

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Singlular (short wind period(s)) are more difficult but there is no more cumulative induced deflection after the initial deflection<HR></BLOCKQUOTE>

I think it's interesting to see the angular change stop after a while. Take a look at the file test_470_10_000_100.txt (link above) and you can see that the bullet is accelerated off course, and then the velocity in the cross wind direction goes to a constant after about 600 yards and the windage MOA stays at 1.4 MOA all the way to 1000 yards (constant anglular deflection).

[ 02-17-2004: Message edited by: JBM ]
__________________
JBM Small Arms Ballistics -- http://www.eskimo.com/~jbm

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