Spin Drift Questions / Solutions ?

[prestonpritchett]

Guys
I am over my head and need advice. I copied some stuff from some different websites on the Magnus and Coriolis effect. I remember the back site on the trapdoors was made at an angle to compensate for part of this. I know that it is not going to be 100% but. We have started making scope rings and I was wondering if because our scope rings have the bubble in them. If when you mounted it on your rifle and took a feeler gage and made sure the gap on the top cap on the left side was the same on the right side. Could you then take a pc of plywood at 100 yards and put a nail in the top portion and tie a string to this with a weight attached so it would be vertical due to gravity. If my 308 drops 39 minutes at 1000 could I drive another nail at 40.83”,39 x 1.047) then measure over to the left 1.1 moa,1.151) because of the data below. Drive another nail here. Now hang my string on this nail and with my bubble straight with the world, cant my scope to match the cant of the string. Would this delete “most” of the effect mentioned below? I


For example,typical 1000 yard small arms trajectory), if you always shoot in the northern hemisphere where the horizontal drift is always to the right, and you have a right twist barrel as most of us do, then your bullet will drift to the right approximately 9' due to gyroscopic drift, and an additional 2.5' due to Coriolis, resulting in 11.5' right drift, even in zero crosswind. ,1moa = 10.47” 1.1 moa =11.51” this is my figures in parenthesis)
http://www.appliedballisticsllc.com/index_files/SpinandCoriolisDrift.htm

 

[mikecr]

Your ring bubble can't be seen from shooting position, especially with that scope mounted so high, so I don't really see how it would work.

 

[Cheechako]

For years I've been sighting my 1000 yard rifles to hit 1' to the left at 100 yards and then fine tuning on an actual target. My ignorant farm-boy brain needs to do things the simple way.

Ray

 

[prestonpritchett]

As far as not seeing the bubble from shooting position I would have to disagree. It is open to your left eye in all the positions I have tried. The scope is mounted high to be in line with a UNS,universal night sight). The stock is one of the first Tac Mods ever built which was a gift from Robbie Johnson. Robbie and Jason StJohn won the Internation Sniper Championship the last 2 years. You can watch them on the military channel. With multiple tours behind his belt has done a fine job in designing the stock for not only prone but multiple position shooting, and also has rails to mount lights, lasors and IR iluminators. The action is the first one we ever built. I didn't figure anyone would want to buy it so I just kept it myself. I mainly posted this to show off our rings. Planning on cutting the barrel off to 20' and installing a Sure Fire suppressor attachment. As far as a war machine I think it would be hard to beat.

 

[CJ6]

Nice looking set up. Steel or Aluminum rings? What height are they? Are those alignment pins,silver) by the capscrews?

 

[prestonpritchett]

CJ6
The first ones are 7075 T6 Aluminum. The Aluminum has a yield strength of 73,000 psi. We will be making some from 4140 PH in the future.
The first ones are
30mm x .875
30mm x 1.0
30mm x 1.125
30mm x 1.250
34mm x 1.0
34mm x 1.125
The Aluminum ones are .950 wide and the steel will be .625 wide.
The silver pins you see are 1/8 dowel pins that keep the clamp square to the ring and at the right height.
The bottom of the ring is machined at the same time as the bore for the scope on a 9 axis machine. This is done in one operation to ensure that the bore is parallel with the bottom of the ring. We checked another brand and found that they were off .0025 in .625 inch. We checked ours and found it to be off .0003 in .950. We machine the locking lug that keeps your ring square in the same operation also.
Thanks
Preston

 

[SomeFool]

Let me first start by saying that I am no expert, and had to read the question several times as well as the attached article. I also had to draw myself a few pictures to convince myself and mean no offense if I misunderstood the question, but here goes.
First off the problem with compensating for spin drift with a straight line,the up and down portion of the reticle) is that the drift is not actually a constant. Think of a pitcher throwing a curve ball, the ball will travel somewhat straight as it leaves the hand but will cut drastically to one side as the velocity and spin ratio falls out of harmony. By that example, the bullet will drift more in the last several hundred yards than it did in the first 700. Also bear in mind that because it is a 'harmony' it can be adjusted by changing the twist rate or velocity.
Now to Coriolis.. Coriolis is not always going to be to the right, it depends on the direction of fire, unless you meant that you would only be shooting in that direction for every, single shot ), and the amount of compensation is mostly due to flight time, compensation = speed of earth rotation * flight time), so if you change your load, that number would also change.
I hope that this helps, and the rings look great, keep up the good work.
Some fool

 

[243Mendoza]

For a thousand yards, just add 1 moa to your windage. If you cant your scope you will mix the elevation and windage effects when you adjust either.

 

[titus123]

The Coriolis effect relates to your global position. i.e if you are in South Africa your rate of given drift would be different than say if you were at home<in your home state>. Also if you are closer to the eqautor the difference in world gyroscopy <magnus effect> would be greatly different. That is more prounanced. Canting you scope will not remove the effect but only make long range hits more difficult because you are in a sense blurring the lines between vertical and horizantal adjustments. Imo your best bet is to crank your windage according to the given requirments of the shot.
Remember Marine Scout/snipers make 1000 meter shots, and they are only concerned with how many moa they need to adjust to hit the target the first shot.
Also as a side note I think your rings are awesome, a self contained bubble level/ scope ring set-up is pure genius. And I will have a pair< aslong as my wife let's me>.