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Do you guys dial in for spin drift?

 
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  #15  
Old 04-27-2011, 10:18 PM
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Re: Do you guys dial in for spin drift?

Is a head wind 180 degrees and a tale wind 0, or do i have that backwards.
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  #16  
Old 04-27-2011, 10:25 PM
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Re: Do you guys dial in for spin drift?

It was actually great to see some one so skilled, spent a 1/2 day with him and it was ballistic bliss, he shot those 2 groups at under 3'' at 1000, then the whole day he was thinking of his next loads because those where different seating and thing, so he was going to re- verify the verify, plus he has a match in a couple weeks. I saw him shoot 45 shots and his largest group 5 @ 5 1/8 '' at 1003.
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  #17  
Old 04-28-2011, 08:28 AM
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Re: Do you guys dial in for spin drift?

Ok, after reviewing the chart a little more closely I thought a headwind would cause greater lift and the bullet would hit high. Likewise, I thought a tailwind decreased bullet lift and caused the bullet to hit low. I specifically remember having this conversation on here some time ago because I thought the whole idea was counter intuitive until someone stated that is why airline pilots like to have a headwind because they get more lift and can take off in a shorter distance. Someone set me straight.
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  #18  
Old 04-28-2011, 09:33 AM
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Re: Do you guys dial in for spin drift?

Col. Hatcher wrote in his notebook that the .30-06 drifted about 1/3 MOA at 1350 yards. So at 1000 yards, the spin drift's only about 1/4th MOA.

I and other long range shooters with high master classifications competing in long range matches use the same windage zero from 100 through 1000 yards. Considering the bullet's trajecory axis changes only about 1.5 degrees from up at the muzzle to down at a 1000-yard target, there's not enough gyroscopic precession working on the bullet over time to drift it very much.

So there's not enough to even measure easily by live firing exercises. How Col. Hatcher got his data is unknown to me.
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Old 04-28-2011, 09:36 AM
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Re: Do you guys dial in for spin drift?

Quote:
Originally Posted by CRNA View Post
Ok, after reviewing the chart a little more closely I thought a headwind would cause greater lift and the bullet would hit high. Likewise, I thought a tailwind decreased bullet lift and caused the bullet to hit low. I specifically remember having this conversation on here some time ago because I thought the whole idea was counter intuitive until someone stated that is why airline pilots like to have a headwind because they get more lift and can take off in a shorter distance. Someone set me straight.
Headwinds slow bullets down, tail winds speed them up. This is what drag does at supersonic speeds of bullets.

Airplanes are way subsonic at take off. They need the increased lift to get them off the ground. The added drag caused by planes taking off into the wind is meaningless to what increased lift does. And some planes add more angle to the wing with flaps that angle down so takeoff at lower speeds will have added lift.
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Old 04-29-2011, 12:56 AM
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Re: Do you guys dial in for spin drift?

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Originally Posted by Bart B View Post
Col. Hatcher wrote in his notebook that the .30-06 drifted about 1/3 MOA at 1350 yards. So at 1000 yards, the spin drift's only about 1/4th MOA.

I and other long range shooters with high master classifications competing in long range matches use the same windage zero from 100 through 1000 yards. Considering the bullet's trajecory axis changes only about 1.5 degrees from up at the muzzle to down at a 1000-yard target, there's not enough gyroscopic precession working on the bullet over time to drift it very much.

So there's not enough to even measure easily by live firing exercises. How Col. Hatcher got his data is unknown to me.
I don't see any consideration on bullet type, velocity, or even the direction of twist, (since coriolis can work against it depending on geographic location.) Blanket statements on a specific chambers isn't an accurate gauge. I myself discovered gyroscopic drift at 400 yards, when the 220gr RN would inexplicably hit 3 inches more to the right, than the 180gr SPs in my 30-06. If I would have realized what was going on beforehand, I would have understood the differences in the POIs at 200 and 300 yards weren't errors in doping wind.

As I've alluded to earlier; since I don't usually shoot very far; I try to make-up for it by shooting small targets... and one doesn't consistently hit a cold-bore shot at the 400 yard 1/2moa target, using the 180gr SPs traveling at 2560fps, in my 1 in 10 right-hand twist 30-06, in central Ohio; if one doesn't take into account the 1/4moa gyroscopic drift... and one will definitely not hit it with the 220gr RN at 2390fps, without accounting for the 1moa adjustment.
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  #21  
Old 04-29-2011, 06:42 AM
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Re: Do you guys dial in for spin drift?

Quote:
Originally Posted by justgoto View Post
I don't see any consideration on bullet type, velocity, or even the direction of twist, (since coriolis can work against it depending on geographic location.)
I've not seen any coriolis effect in either hemisphere from South Africa at 30 degrees south latitude to the Washington, DC area at about 40 degrees north latitude. Nobody else has either shooting their 30 (and smaller) calibers through 1000 yards. Shipboard naval gun fire computers I worked on had zero correction for both spin drift and coriolis up through 4000 yards; beyond that it grew a little bit for each 1000 yards of range.

Quote:
Blanket statements on a specific chambers isn't an accurate gauge.
I think they're fine when the best long range marksman on earth in International Palma competition all agree there's no significant effect.

Looks like your next quote's a blanket statement.

Quote:
I myself discovered gyroscopic drift at 400 yards, when the 220gr RN would inexplicably hit 3 inches more to the right, than the 180gr SPs in my 30-06. If I would have realized what was going on beforehand, I would have understood the differences in the POIs at 200 and 300 yards weren't errors in doping wind.
Are you convinced there wasn't a subtle crosswind invisible to the naked eye that caused that windage error? Did you do anything to see how much cross wind there was? And if you were shooting right-handed holding the rifle to your shoulder as it rested atop somthing on a bench, it's normal that heavier recoiling rounds shoot further to the right. The barrel moves that way while the bullet's going down the barrel.

David Tubb (many time Nat'l champ, US Palma Team member) didn't see any spin drift effect shooting 250-gr. bullets leaving at 2150 fps from his .308 Win. at 800 through 1000 yard targets in all directions. I specifically asked him about that at a match when I learned he used them. The rest of us used 190's or 200's and we didn't see any effect. But his 250's bucked the wind better than our lighter bullets leaving faster.

Quote:
...and one doesn't consistently hit a cold-bore shot at the 400 yard 1/2moa target, using the 180gr SPs traveling at 2560fps, in my 1 in 10 right-hand twist 30-06, in central Ohio; if one doesn't take into account the 1/4moa gyroscopic drift... and one will definitely not hit it with the 220gr RN at 2390fps, without accounting for the 1moa adjustment.
I and many others see no difference between the first shot from a cold bore to the 10th through 20th when the bore's very, very hot.

Spin drift ain't linear from zero to many yards down range. If it's 1/4th MOA at 1000 yards, it will be about 1/10th MOA (probably less) at 400. Spin drift's almost directly proportonal to the spinning object's spin axis angle change or drop per hundred yards. There's very little change from 0 to 400, quite a lot from 0 to 1000.

======================================

I know some folks are convinced that coriolis and spin drift are very noticable in their shooting events. Having shot with, and been one of, and sometimes out shot, the top ranked long range competitors in the USA (world, too, in International Palma and Goodwill Matches), none of us ever use, think about, discuss, adust for, nor even care about.....spin drift or coriolis. 'Tain't enough to be concerned about.

Last edited by Bart B; 04-29-2011 at 06:51 AM.
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