9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

[Bart B]

Having shot both smallbore matches at 100 yards and 30 caliber matches at 1000, the wind drift is equal for both right and left hand winds. But the elevation change is quite different.

Smallbore, .22 rimfire standard velocity bullets with right hand twist track across the target from a bit more than 10-o'clock to a bit more than 4-o'clock. The string up and to the left from right hand winds and down and to the right for left hand winds. It's about a 3:1 ratio

30 caliber rounds leaving at 2500 to 3100 fps from right hand twists track across the target from about 9:10 o'clock to 3:10 o'clock. The string the same as rimfire .22 ammo, but not nearly as much; about a 15:1 or 20:1 ratio. I've made as much as 5 MOA wind correction to the right to 5 MOA to the left when the wind direction changed sides with 30 calibers at 1000 yards and not seen any change in vertical impact. It ain't much to be concerned about.

Coriolis effects with 30 calibers isn't enough for me to be concerned with. Most of its masked by the accuracy levels us humans shoot coupled with subtle air movements and therefore's very hard to measure and not typically noticed.

 

[Topshot]

One thing I have noticed with target shooters. They put almost no thought into spin and coriolis drift. Target shooters get sighter shots before the scoring shots. So it is not a huge concern.

ELR Field shooters are the main ones that take spin and coriolis drift seriously.

 

[Bart B]

One thing I have noticed with target shooters. They put almost no thought into spin and coriolis drift. Target shooters get sighter shots before the scoring shots. So it is not a huge concern.

Target shooters do not always get sighting shots before the scoring starts. In many individual and team matches, no sighters are allowed. Besides, they've all got windage zeros for all the ranges they shoot at; for some it stays the same but for others it changes. M1 and M14 rifles often have windage zeros change with range.

Rarely is their sight's elevation adjustment axis (nor anyone elses, for that matter) perfectly aligned in the plane between the bore axis and sight axis. And even when it is, the horizontal direction the bore points to when the bullet exits is different than when the round's fired and the bullet leaves the case mouth. And that varies with the shooting position.

There might be 5 people on this planet who can judge cross wind values accurate enough to put the first shot within 1/2 MOA of point of aim at long range with cross winds less than 5 mph. I'm not one of them. There's too many other subtle cross wind values between shooter and target that are invisible to even the aided eye. These conditions mask any coriolis drift and sight elevation axis errors that exist. So how anyone can separate on-target results into which ones' horizontal error was cause by what is something to consider. This is the main reason the top long range rifle team coaches don't concern themselves with coriolis effects. Even when the bullet fired drifts only 6 inches per mph of uniform crosswind at 1000 yards.

 

[ken snyder]

Bart B nailed it right on the head for me and what I do. My LR Rifles do not have the cross hairs level they are slightly twisted to compensate! Kind of funny for those of us that do this we will tell you that our scopes are not on out of level your scope that is mounted level is crooked.

 

[paphil]

I agree on the twisted scope theory! I have my guns scopes canted 2 degrees, to the left. That is done to compensate for spin drift. I am allowing enough cant for about 8" at 1000 yards. The scope leans left about 1/2 bubble and I use the level to shoot and not the reticle to allign my shot. I did this because I don't use a calculator to dope the wind, I use the numbers in the top ring on the Huskemaw turret. I got tired of missing in 3mph wind conditions and holding 1 moa for a left wind and 3 moa for a right wind. There is a vertical component for left and right and in my experience , it is most noticable in the first 4-5 moa and then seems to taper off. I hold about 1/3 moa(1 click) of vertical for each 2 moa up to 6moa and then nothing after that. Shooting east and west, at 1000 , I add a click for west and take off for east. It is only about 3" difference each way and my range is north/south so my gun falls in the middle. Most of this stuff doesn't matter at all for the average gun but when you get a good one that shoots 4" groups at 1000 yards it will all make sense!

 

[Bart B]

I agree on the twisted scope theory! I have my guns scopes canted 2 degrees, to the left. That is done to compensate for spin drift. I am allowing enough cant for about 8" at 1000 yards. .....Most of this stuff doesn't matter at all for the average gun but when you get a good one that shoots 4" groups at 1000 yards it will all make sense!

Welll now, let's see if 2 degrees cant on a scope's vertical adjustment axis is correct......

So, if your rifle's bullets need a 2 degree cant to move impact 8 inches horizontally, those bullets have to drop only 229 inches at 1000 yards; 229 x (sine of 2 degrees) equals 8.

What bullet and muzzle velocity do you get to do this? That's the flattest shooting rifle I know of if it needs about 23 MOA of elevation come up from boresight to do that.

My long range target rifles also shoots 4 inch groups at 1000; but only once in a while just like all other super accurate rifles. But I don't worry about coriolis so I must be mentally deranged.

 

[Michael Eichele]

I have been blessed enough to have done some testing and development at a full 1K with ZERO wind. I say zero because the air was dead still at my end and the minor mirage indicated zero movement. Also, when checking the target there was no movement to confirm this. What I can say is that even with different rifles and scopes on different days or even years, they have all had one thing in common. Dead nut zeros at 300 yards and anywhere from 9"-12" (Depending on the load) bullet impacts to the right at 1K. Spin drift and/or coriolus is not a myth or anything new. They are both proven, calculatable AND predictable. Yes, it takes very accurate 1K rifles to be able to detect this. Fortunately, I have also been blessed enough to have rifles that would shoot as well as .35-5 MOA at a full 1K in a no wind condition. IMHO this type pf accuracy along with consistency is more than enough to be able to detect anything but a dead nut zero at 1K.

I have done as Bart B and ken have in the past and 'canted' my scopes a bit. Now I level them. All of my software including my field software take into account all the variables and I just dial the numbers wind or no wind. That may not be for everybody but it works for me.

 

[Michael Eichele]

I know for my rifles, 2 degrees would work for one and 1.25-1.5 MAX would work for the other.

For a 300 grain hybrid starting out at 2750 FPS 2 degrees of cant = about 11" at 1K. Which also = 23 MOA. Fo rmy 308 it is more like 14" at 2 degrees of cant with over 31 MOA.

 

[Bart B]

All of my software including my field software take into account all the variables and I just dial the numbers wind or no wind. That may not be for everybody but it works for me.

How do you measure the cross winds in each of the ten 100-yard segments from zero to 1000 yards? Or even each third of the range? There's a big difference in on-target wind deflection depending on the wind in each of these range bands.

This I gotta know 'cause I don't know of anyone who can do this to end up with less than 1/2 MOA error at 1000.

 

[Michael Eichele]

How do you measure the cross winds in each of the ten 100-yard segments from zero to 1000 yards? Or even each third of the range? There's a big difference in on-target wind deflection depending on the wind in each of these range bands.

This I gotta know 'cause I don't know of anyone who can do this to end up with less than 1/2 MOA error at 1000.

No one ever said anybody including myself can do this perfectly. Thats not the point. You do the best you can with what you have at the time.

Some things I have used in the past is dust, fog, rain or snow, mirage, cotton wood seeds etc....Also, where I hunt mountain sheep and goats, the air movement is VERY predictable in relation to the time of day AND the layout of the land. The thermals up here are scary predictable.

The one time I was hunting where the wind was not behaving as typical thermals there was cotton wood seeds blowing up and down every small drainage. My cousin was setting up on a moose at 604 yards. Looking through the spotting scope I could see which direction and how fast the wind was blowing at 3-4 locations between us and the moose. I called the wind and he drilled him through the crosshairs with one shot.

Use what you can at the time and that is all anybody can do.

In another instance, I was able to use small patches of fog roll through the drainage where I was on one side and my dall ram was on the other. 763 yards. Again, I was able to see the speed and direction. Again, I one shot deal. Was I able to see every 100 yard segment? No. I just used what I had at the time.

I cant say I have never missed on the first shot from wind miss-judgements, I just do the best I can with what I have at the time. Fortunately, at those ranges, you can typically get back on target before bullet impact to see where you went wrong and you get anoth chance most of the time.

 

[Bart B]

For those interested, horizontal shift of bullet impact due to cant equals sine of cant angle multiplied by bullet drop at target range.

 

[Bart B]

In another instance, I was able to use small patches of fog roll through the drainage where I was on one side and my dall ram was on the other. 763 yards. Again, I was able to see the speed and direction.

How were you able to see the speed? Or how did you calculate it?

 

[Michael Eichele]

How were you able to see the speed? Or how did you calculate it?

I could see it. Measure it? Not at that range. This is why we call it judging the wind. We do the best we can with what we have at the time. This is all we can do when hunting. After all this is hunting site and not a match shooting website. Can you judge a car's speed when you see it move? If not, then I can understand why you are so baffled by my techniques. Is this going to happen with exact precision? No. Thankfully a kill zone is bigger than a couple inches.

The bottom line is that we judge and calculate. Coupled with the most accurate loads possible and the highest BC bullets possible, most of the time it works and works well I might add. This is how we do it. If you have a better or more accurate way without setting up wind flags between me and my game, I am all ears.

If you can't do it with regularity and have to prove me wrong, be my guest and come prove me wrong.

You can nit pick me apart all day if you want. I am good at what I do. I have alot of dead sheep, moose, deer and goats on the wall (quite a few killed at long range) to prove it.

Before this gets heated and out of control, I will sign off and out on this subject.

 

[ken snyder]

I don't think that it is at all unusual to find different ways of managing spin drift. The common factor is that something is being done about it. After the first shot we are practicing general non competitive target shooting anyhow.

I cant tell you how many degrees I have my scope canted but it does agree with the rifles intended ranges and I don't suppose that this would be useful with a computer program that takes everything into consideration. I still make my own charts and use the old school rules of thumb probably the same ones that your Grandfathers used. These rules of thumb don't make anything perfect but they do take a large bite out of the concern. Even at that one of the rules of thumb I use is a question: "How far can a dog run into the woods, If that dog were a rule of thumb it could only run half way into the woods because then it's running back out again!