Windage dead calm at 1000

[whatsupdoc]

Been out to 1000 a bunch of times, I noticed that even on dead calm days I need to dial or hold .4 to .5 mills left at 1000.
The scope is dead level and tracks fine.
Wondering maybe my head is not screwed on straight.
What do you think?

 

[plidenbrock]

You probably already know this, so the answer might lie elsewhere, but I assume you already corrected for spin drift and coriolis effects on your bullet?

Obviously it depends on your exact firing latitude, and your barrel's twist. If your barrel is R twist, you would have to hold left, and that would likely be the bulk of your correction. Depending on your latitude, coriolis can cause lateral drifts of varying magnitude, although not huge at that shortish range.

Both of those would require a leftward correction.

Can you specify your barrel twist rate and latitude at your range?

If you've already accounted for those, then I will watch and learn as well. Forgive spelling lol

 

[Deleted member 113831]

Been out to 1000 a bunch of times, I noticed that even on dead calm days I need to dial or hold .4 to .5 mills left at 1000.
The scope is dead level and tracks fine.
Wondering maybe my head is not screwed on straight.
What do you think?

Depending on the particulars, something like .2 or .3 of that will be spin drift.

 

[whatsupdoc]

6.5 creedmoor, 140 hybrid 1:8 twist, Latitude is 42 N.
My ballistic app claims .16 mil correction.

 

[lash]

And you know for sure that it is dead calm for all 1000 yards? Any mirage?

 

[Sniper266]

What does the calculator come up with for a 1-2mph wind? Could just be some very slight wind down range?

 

[Milo 2.5]

The first time I shot 1K, 6.5x284, 130 vld, in a light drizzle, coming straight down, shooting due north, at the time I had never heard of spin drift or Coriolis, I aimed center plate, no hold and drilled center, same at 800 & 900. I've learned quite a bit since, and have done the same since. Today we shoot NNE on the same range. I guess what I am trying to say is we assume no air movement, but I think that is impossible. On what I think are calm days, I will hold half moa or .2 left and be close.

 

[plidenbrock]

6.5 creedmoor, 140 hybrid 1:8 twist, Latitude is 42 N.
My ballistic app claims .16 mil correction.

Assuming that's a right hand twist, correct?

Do you know what the .16m correction is for? That's an awful small total correction for both spin drift and coriolis at that range, assuming a truly no-wind situation and right-hand twist.

If you're using an electronic gadget to obtain your firing solution then input errors can sometimes unintentionally arise, for example if you have a R twist that is accidentally entered as a L twist, that sort of thing.

Assuming all those other factors are accounted for properly, then the only other thing that might explain things would be an error in your scope mounting. IE a perfectly functioning scope mounted at a tiny cant would also account for a consistent lateral drift at distance, assuming you're indexing your turrets and not holding over.

 

[Deleted member 113831]

6.5 creedmoor, 140 hybrid 1:8 twist, Latitude is 42 N.
My ballistic app claims .16 mil correction.

That is pretty close. The rest could be shooter, an ever so slight breeze (1mph = .2 with that combo you have), or a slight optical effect. No way to really know without being there with you.

 

[Milo 2.5]

Assuming all those other factors are accounted for properly, then the only other thing that might explain things would be an error in your scope mounting. IE a perfectly functioning scope mounted at a tiny cant would also account for a consistent lateral drift at distance, assuming you're indexing your turrets and not holding over.

I have to laugh, trigger pull too can affect it. I shoot with a guy I swear has 3/4 moa left built into his zero for trigger pull. Actually he doesn't, I've checked his zero with myself shooting, but we run basically identical rigs, loads etc.. We'll be shooting plate and the question of wind hold will come up, he is always holding or dialing more left wind, or less right wind than I am. It has to be trigger control.

 

[whatsupdoc]

Right twist.

Calc gives me .55 mill correction for 2mph wind 90 degrees to bullet path.
Is it possible that there is a slight breeze sure, the windsock at 1000 did not show it.

I will check the settings on my app and see.

The reticle is dead level, I used a plumb line and a home made light that projects the reticle onto a white board.

 

[lash]

That is pretty close. The rest could be shooter, an ever so slight breeze (1mph = .2 with that combo you have), or a slight optical effect. No way to really know without being there with you.

^^^This^^^
I'm personally not good enough to detect a 1-2 mph breeze at 1000 yards unless it's right at my firing position.

 

[whatsupdoc]

I have to laugh, trigger pull too can affect it. I shoot with a guy I swear has 3/4 moa left built into his zero for trigger pull. Actually he doesn't, I've checked his zero with myself shooting, but we run basically identical rigs, loads etc.. We'll be shooting plate and the question of wind hold will come up, he is always holding or dialing more left wind, or less right wind than I am. It has to be trigger control.

It could be recoil management also.

I dont think it was trigger control, yesterday made 11 out of 12 hits on a 10" plate at 1001 yards.
Thats how I know there was no wind, because if there was wind that would NEVER happen.

 

[Milo 2.5]

It could be recoil management also.

I dont think it was trigger control, yesterday made 11 out of 12 hits on a 10" plate at 1001 yards.
Thats how I know there was no wind, because if there was wind that would NEVER happen.

I was in no way implying that was your issue,, we were discussing possible causes. I think you are under estimating your abilities though on no wind, bet you could do equally as well in a 5mph wind if constant.

 

[tnichols]

Good input above. Here in Hooterville, it’s extremely rare to not have a dab of wind at 1K. It’s your job to find it ?. If I think it’s dead calm I’ll go with 0.1 mil left to compensate for spin. The calc usually asks for 0.2 for spin, and that seems to be just a bit much.

 

[steve123]

I zero my rifle favoring the left, it's usually .05 mil to .1.

That takes care of most of the Spin D.

Before I started compensating with my zero this happened. During a match two friends and I chose to shoot at the 1000Y plate for the whole stage because it was worth more points. There were good wind flags on the range with the wind mostly coming from our back at 3-5 mph. We were next to each other and together noticed that when the flags were going to the right we had to aim .2 mil more left to get a center hit vs the wind coming from the opposite direction.

Since then I favor left in a left to right, if only .1 mil.

 

[Lowlight]

trigger control,

bet you are a right-handed shooters you would need about .2 mil if you wanted to call it SD, another .2 is you.

 

[whatsupdoc]

I definitely appreciate the comments and suggestions from everybody as its part of the learning.

The reason I even asked the question is typically where I shoot there is some wind and I deal with it, but a few days ago it was dead calm and it
surprised me that I had to hold .4-.5 left. There were only two new shooters there so there was no asking someone.

Will see next time with a different rig.

 

[Lowlight]

Dead Calm is usually an error, there is almost always something.

At the Range in AK, we have very, very light winds, 1 to 2 MPH on average. And there are times when guys will call it dead calm or no wind when in fact there is a bit a wind. (It's always left to right too)

A 1 MPH wind at 1000 yards is more than SD and usually most miss this. Don't forget the round is going about 14ft above the line of sight so even if you don't see it move anything, it's still there. Less resistance as it's off the ground.

Last class Marc was calling no wind early in the AM but it was still there, edge of plate or .2 mils is pretty common. You really need to focus in on mirage when it's that light because nothing else may move or register and if your position is being blocked so it appears to be nothing, the distance between you and the target may still have something

Wind downrange is the hardest to call because it is invisible and unless it moves something you don't know it there

PS how can anyone claim Coriolis and then say it was a NO WIND conditions, Coriolis is responsible for winds too.

 

[ShooterwithNoName]

Been practicing reading mirage today. Been a great day for it here in WV. I've noticed that the mirage through my scope and spotter just barely tilting left to right. I've even seen it leaning to nearly 45deg with absolutely no sign on any trees, grass, shrubs, nothing. All looks dead calm but I can feel it here at my shooting position. I can see even when the mirage appears to be nearly vertical it's still moving left to right a bit. As I move my spotter up into where the bullet path would be at 750yds the higher I get off the ground, the more the mirage moves. I can see the difference the terrain makes on it from ground level to about 10' above.

I've been at it for a couple hours just watching thru the glass. It's TRUE even with mirage rising at 90deg at ground level, its moving left to right at about 6' and above. Pretty cool, I'm just learning to read mirage and its awesome to see it in action and begin to understand it.

 

[Deleted member 113831]

Been practicing reading mirage today. Been a great day for it here in WV. I've noticed that the mirage through my scope and spotter just barely tilting left to right. I've even seen it leaning to nearly 45deg with absolutely no sign on any trees, grass, shrubs, nothing. All looks dead calm but I can feel it here at my shooting position. I can see even when the mirage appears to be nearly vertical it's still moving left to right a bit. As I move my spotter up into where the bullet path would be at 750yds the higher I get off the ground, the more the mirage moves. I can see the difference the terrain makes on it from ground level to about 10' above.

I've been at it for a couple hours just watching thru the glass. It's TRUE even with mirage rising at 90deg at ground level, its moving left to right at about 6' and above. Pretty cool, I'm just learning to read mirage and its awesome to see it in action and begin to understand it.

You will run across this eventually anyway, so I'll just tell you now. A switching tail wind or head wind is the most frustrating wind to shoot in. Not only does the wind switch right to left quickly enough that it is hard to break a shot in the the same condition everytime, but the optical effect increases the magnitude of the error.

You might be dealing with say a mild 2-3mph wind switching left and right, so you do your wind math and determine that as long as you hold center you won't be pushed off the plate. But when you shoot it, you are missing 0.2-0.3mils off one side, then the same off other side. This happens because it isn't only the wind you are dealing with.

No, I don't have any rock solid rules of thumb to predict it before hand. Just tuck away the knowledge so that when you see it, you won't go nuts trying to figure it out.

 

[Greg Langelius *]

I have a personal term for the undefined but discrete distance between muzzle and target.

XTOF = Across the Time of Flight. Describes it without defining it.

Mirage is probably your only friend in calmer conditions, XTOF.

Always listen to LL. Some weeks he shoots more LR and ELR than many of us may do in a lifetime.

Greg