Re: Spindrift Calculation??
Allow me to explain the reason for addressing spin drift another way...
You have 7 components of horizontal possible error:
1. Wind drift.
2. Spin Drift
3. Coriolis
4. Air temp effects on 1 and 2
5. BP effects on 1 and 2
6. Projectile stability error on all of them.
7. SHOOTER induced error on all of them.
Consider that you can only do something about 1, 2, 3, 4, and 6. Less so on 4 and 6. We agree that you don't shoot to a POINT of attack on any target, you shoot to a circular error of probability. For the sake of discussion, say this CEP is 10" (generous number) at 1000 yards.
A shooter is not correcting his sights to put the "desired point of impact" on the center of the target, but the shooter is desiring to keep that 10" circle in the center of the target. On a 1000 yd bull, that's the entire diameter of the X ring, which out of 20 shots is the max number most shooters go for, last record I am aware of is a perfect 200 score with 18 Xs? SO, keeping in mind that the 10" circle in the center of the tareget is the goal, OR, your bullet might strike along the side of that 10" error CEP.
By allowing "slop" to enter the formula, or ignoring errors that you CAN correct for, you simply give away more than half of that 10" CEP. For a 175 gr. SMK out of the M-24, the spin drift is 11.43" measured by Doppler in 2001. By ignoring the first component of horizontal error, the shooter is "Giving away" half of his ability to "center up the shot".
NOW, combine this error, with a error in assessing the wind downrange in the direction of drift (left to right), you now, are allowing yourself even LESS error in determining the wind. Don't take this wrong, BUT, i've seen years and years of using HISTORICAL data not DETERMINING data used to make long range shots, and the historical data falls down nearly every time. Historical data cannot account for air conditions in my experience, unless you are talking match shooters that shoot a circuit that is roughly the same time of the year and rarely do those shots reach into the near subsonic range. Even at 1000 yards, competitors are using guns that go supersonic for another 300-500 yards typically.
The guys that shoot 1000 yards with 308 guns, Palma guys, see the minute error effects of ignoring those conditions. Mr. Art Sievers, who coached the 1969 Palma gold medal team definately addressed spin drift, he didn't know it was that, but he knew that in a no wind condition, he would put "x" MOA on his rifle team's sights at 800, 900 and 1000 yards. I'm a perfectionist, I don't and won't ignore any factor that can be accounted for or corrected for.
I'd suggest that if these small things are ignorable, the situation isn't reaching into the last 10% of the gun's supersonic range. But then again, that's why alot of competitors us technology, hotrod guns, hotrod bullets ,etc. to give them the edge and the ability to ignore the 2% conditions that cause misses and 10s instead of Xs.
Humbly,
Trigger
ps.. in the following video, without 2.00 MOA of left drift, this 25" wide target would have been MISSED.
MK 211 STRIKE FROM 1560 METERS... SPIN DRIFT INCLUDED, NO WIND