Ok folks, here is a new topic that should get some mental smoke going.
The snipers nightmare. Every piece of data I have looked at in the last two day gives conflicting information.
Example: For a given bullet I have found 6 different adjustment values for a 10 mph full value wind @ 1000 yards! The barrel length was the same and the muzzle velocity was with in 50fps.
Marines constant method: 10 moa
Army chart: 5.5 moa
1/2 minute Rossette chart: 5 moa
1 minute Rossette chart: 7 moa.
Sierra ballistic program: 9 moa
Plus another one I forgot that but it at 8 moa!
So Gooch, Rick, and any other old timer with a TON of trigger time,
what gives? How can All of these be correct?
USA - Thursday, October 08, 1998 at 16:22:09 (EDT)
Scott - On the wind formula, they can't all be correct. The problem comes about due to using different drag co-efficents in the orignal model. Since the Marine answer is 10 moa, I must assume that you are talking 168 gr. At SOTIC use a constant of 10 for the formula and while not dead on it is within .5 moa at that range. If the G1 model is used you will get one answer and if you use the correct boat tail co-efficent you will get another. The rossettes were modeled on a multiple constant that had a basic flaw and gave way toa low of a moa adjustment. The Sierra program uses the G1 drag and comes up about 1.5 moa short. The army figures compute, by error, to be .5 increments instead of 1 moa increments. So double the army answer and you are close. I know, I really didn't answer your question, but that's as close as I can come. I do know that if you use wind speed in knots, times range in hundreds, divided by the constant of ten, you will have a moa adjustment that will hit a mansized target at 1000 yards. Use the same formula from 100 to 1000 and you will start out being .5 moa too strong and end being .5 moa too weak. But, hey what's .5 inches to 5 inches among friends? By the way, don't forget spin drift.
Fayetteville, NC USA - Thursday, October 08, 1998 at 23:01:47 (EDT)
On the windage issue. I have one thing to say. Remember guys all of these formulas, charts etc are based on a crosswind with a single component in "standard" conditions. We all know that it is a crap shoot. Gooch's best advise is to shoot a lot, learn to read mirage and bury a lot of chicken bones.
Damn, I'll try to get serious here.
All of the wind charts are only an attempt to get the shooter on paper. No one can look at a chart and punch out X's all day just as I can't read a book on nuclear physics and build an ion drive for a space ship (where is he going with this huh?). Anyway, when I am shooting a lot, I can usually look at the mirage or the observable conditions and be pretty close on a wind call. If I haven't been shooting a lot, then I might as well go with the voodoo.
Rick is on target with his suggestions on this so I will just shut up and retire to my rack! Thanks Rick. I miss our IM's since I have had to start this totally, bullshit civvy job.
Gooch is out of here!
Sherwood, AR USA - Friday, October 09, 1998 at 02:16:40 (EDT)
Using the Marine constant formula, C=10 gives you an answer in clicks with 1 clk= .5 MOA (ie: M3A scopes) NOT in MOA. For MOA use C=20. These give result very close to the chart in FM23-10, which I have found to be quite accurate, given the limitations of all charts.
Of course this is for M-118 only.
Also spin drift is no joke. It has bitten me more than once.
E Engler <firstname.lastname@example.org>
CP Greaves, ROK - Friday, October 09, 1998 at 04:42:05 (EDT)
Rick, thanks for the reply. The thing that makes the windage issue so "interesting" is that at times I have used several of these formulas and had center mass hits with them all, both in competition and on the UKD range. What this tells me is that my wind estimation was OFF and I was essentially just getting lucky. Example: The Army chart gives 4.5 minutes for a full value 10 mph wind at 800 Meters. I have used that figure repeatedly to ding the target. Yet when compared to the balistic program for the same round, that call is off. So my assumption is that my wind call was actually off. This is kind of like voodoo! Why is this bugging me right now? I am trying to develop an accurate wind chart for my 26" PSS. Gathering all the various data has brought to light (at least for me) all the varying data out there. Guess I'll just have to stick with the Sierra program as verifying the windage for every 100 yards and every 3 mph all the way to 1000 would take a life time in waiting for each condition.
USA - Friday, October 09, 1998 at 09:16:48 (EDT)
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