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Long Range shots - elevation right on always to the right

 
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  #15  
Old 08-24-2011, 01:26 AM
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Re: Long Range shots - elevation right on always to the right

NVH1,
You should expect to experience 6-8 inches of rightward drift at 1000 yards from a right twist barrel due to "Spin Drift". It's caused by the high speed rotation imparted to the bullet by the bore's rifling. If you live in the Northern Hemisphere, depending your direction of fire (azimuth of fire), you could expect to experience an additional 2 inches of additional rightward drift due to the rotation of the earth - a result of the Coriolis effect, often referred to as Coriolis Drift.

These sources of drift should be experienced even if all of your equipment is set up exactly plumb with the world. Even if you've done everything exactly perfect & correct. Believe me. I've been there, done that. You will run into those that say it isn't so. Be cordial, and then dismiss everything else those individuals have to say concerning this matter.

They're disregarding facts of life as they exist on this planet, as proven by the best and brightest minds. NASA and the US military incorporate corrections for this as a standard operating procedure. So unless you believe they're full of __it, you'd best believe, study, learn, and adjust.

You'll find others that ask; is it significant to be worth correcting for when a 1 mph cross wind-caused drift at 1000 yards can be the equal in magnitude. You'll have to answer that for yourself. Spin drift occurs with a specific bullet out of the same rifle to the same exact magnitude with each and every shot. Would you ignore the comparative drift if the source was a 'known' 1 mph cross wind. If you would, then you'd have to be happy with an aiming error of ~6-8 inches at 1000 yards.

Now I agree it's also important to have the rifle scope tube mounted parallel with the rifled action, and the cross hairs in the scope aligned vertically with Earth's gravitational pull. But understand with all else being correctly accounted for, you WILL experience a rightward drift from a right twist rifled barrel of approximately 6-8 inches over a distance of 1000 yards due to the bullet's rotational spin on each and every shot fired. And Coriolis Drift in the northern hemisphere could add another ~2 inches of rightward drift.

So the majority of the drift you're experiencing is to be expected. There may be some additional rightward drift being added due to equipment setup. You should be feeling good about life. Much better than if you weren't observing any rightward drift. It's a fact of life. There are ways to account for it. If you're only shooting at game with kill areas substantially larger than the magnitudes of these sources of drift, then you can zero about 1 inch left at 100 yds, and split the difference in the left-right error that will occur over the 1000 yards. If you're targeting itsy bitsy voles, then you'll pretty much have to add the dope for Spin and Coriolis drift on each and every shot.

I've spent days researching these topics, and finally came to peace with them.

Last edited by phorwath; 08-24-2011 at 03:20 PM.
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  #16  
Old 08-24-2011, 06:10 AM
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Re: Long Range shots - elevation right on always to the right

Paul, that's one of the best explaination of those effects I have ever seen. Good job. Still want to see pics of stuff that the Leica1600 helps you take this season.
Later
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  #17  
Old 08-24-2011, 09:54 PM
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Re: Long Range shots - elevation right on always to the right

Hi Guys, thanks for all the input, I did try the weighted string at 100 yards, put the level in the action and on the scope and all 3 where right on. Also put an 8' contractors level vertically at 100 yards same result. No decernable cant in the reticle. At at 100 yards I shoot 3/4" LEFT go figure.
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  #18  
Old 08-24-2011, 09:59 PM
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Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by NVHunter1 View Post
Hi Guys, thanks for all the input, I did try the weighted string at 100 yards, put the level in the action and on the scope and all 3 where right on. Also put an 8' contractors level vertically at 100 yards same result. No decernable cant in the reticle. At at 100 yards I shoot 3/4" LEFT go figure.
I'd say call Huskemaw and see if they have any ideas.

However I'm still thinking there's possibly some yaw in how your scope is mounted.

Like the others I don't think it's very likely that your problem comes from spin drift alone. For one it's not consistent enough, and two, it's more than it should bie for spin drift alone.

Do you have a one piece or two piece mount?
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  #19  
Old 08-24-2011, 10:02 PM
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Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by phorwath View Post
You've just discovered spin drift and Coriolis drift.

There are lots of historical Threads covering these topics. If you use the Search feature, you should find a day's or more reading material.
Unless you are shooting something extremely slow the Coriolis effect is not going to have any measurable effect at ranges of under one mile.


Coriolis Effect
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  #20  
Old 08-24-2011, 11:56 PM
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Re: Long Range shots - elevation right on always to the right

My last effort to assist:

I just analyzed your bullet and load using Patagonia Ballistics LoadBase3.0 ballistics software.
Spin Drift: Input Parameters
200 gr Nosler Accubond
3000 fps
G1 BC=0.588
Bullet length=1.49"
10:1 rifling twist rate
Rifle Zero Point = 100 yds
Environmental Conditions= ICAO Standard Conditions.

Spin Drift at 1000 yds = 6.6 inches rightward drift from right twist rifled barrel

Coriolis Drift: Input Parameters
Location = 45 Degrees North Latitude
Direction of Fire = Due East or Due West (90 or 270 Degree Azimuth)

Coriolis Drift at 1000 yds = 2.5 inches rightward drift
Combined, a total of 9.1 inches of rightward drift at 1000 yds

Do as you will with Spin Drift and Coriolis Drift. You can throw them out with the trash and keep re-mounting your scope until you've stripped the base and ring screws free of any remaining threads. But this isn't witchcraft, and you'll never rid yourself of these two sources of bullet drift.

With respect to the prior Post: 1000 yds is a lot less than one mile. I can measure 2.5 inches of Coriolis Drift on target without a magnifying glass. I consider 2.5 inches of 'known' drift to be a measurable effect on my predictive 1000 yard dope.

For the curious... At a distance of one mile there would be 8.8 inches of Coriolis caused rightward drift. Spin Drift is 33.4 inches at one mile.
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  #21  
Old 08-25-2011, 12:09 AM
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Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by NVHunter1 View Post
Hi Guys, thanks for all the input, I did try the weighted string at 100 yards, put the level in the action and on the scope and all 3 where right on. Also put an 8' contractors level vertically at 100 yards same result. No decernable cant in the reticle. At at 100 yards I shoot 3/4" LEFT go figure.
Take a compass out to where you are shooting, and shoot a line to Magnetic North.

Now shoot a line directly to your target.

Are you shooting along a direct N-S Axis? If not how far off of a direct N-S Axis?
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