Am I Missing From Mirage?

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Husqvarna372

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I was out shooting with a friend trying to hit a 6 inch steel circle up to 500 yards. I have my dope chart and I've had enough success using the formulas on it that I trust what its telling me. Im shooting 168 gr. Hornady Match .308 and regularly getting 1 inch groups or less, with half inch not being uncommon. Optic is a Vortex Diamondback Tactical 4-16x44 FFP, and so far its awesome!
My problem on the last outting is that I seem to be hitting 1 to 2 feet high at 500. Ive shot the 500 before without a problem using the same dope chart and I can hit it with consecutive shots normally. The temperature was -20 C and there wasnt even a whisper of wind. I was nailing the steel consecutively at 450 yards, but as soon as I moved back to 500 and adjusted my scope I would hit 2 feet high. I brought the scope down 8 clicks (mil) and it was still very high and way off from what my dope says. Move back to 450 and Its bang on again. There is only one variable that I can think of and that is mirage, possibly? The difference between the 450 and 500 mark was that I had a very clear view of the target at 450, but once I moved to 500 I could barely see the steel as there was a hump about in the field about halfway between me and the target. I was shooting prone, so in my view I could just barely see the steel and it appeared as if the steel was "touching" the hump in the ground. I could see a bit of heat mirage coming off the snow, Im guessing heat absorption or relfection from the sun? And some heat mirage from my barrel. Is this mirage causing my target to appear higher than what it actually is? Is the image of my target bending over the curvature of the hump in the ground? I wasnt able to move to higher ground to get a good visual on my steel at 500, so shooting 6 inches above the dirt was the only option i had to reach that range. I was on a small hill at 450 so I didnt have the visual problem. what do you think?
 
What is your twist rate?

Jerry

In case you are not sure why I would ask... play out your thought on mirage... what is mirage? what does it tell you about the air you are shooting through? what is the MPH range that mirage is visible?

Figure out how fast the air must be moving to displace your bullet a couple of feet over 50yds of flight.

Plan B, got another scope you can try?
 
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I have done alot of winter trekking on snowshoes and skis on frozen lakes. I have seen incredible instances of mirage of elevated objects at distance when one gets low to the snow surface on sunny days and sights along that surface. I am talking vertical movement easily of a meter or more of distant objects, plus random elevated shapes created by the mirage. I have also seen this mirage elevation effect of distance objects on big lakes when canoeing on sunny days. And I am sure everyone has seen the heat wave mirage coming off road surfaces when its sunny. Your prone position level and low with the snow, and the 2 foot error in sight image and impact is not surprising to me, and so I think your mirage hypothesis is a good one.

You might be able to avoid it by trying a higher shooting angle? Perhaps standing with rifle supported on a sturdy tripod with bag on the apex, to get elevated above that crazy mirage zone along the snow surface. Good luck, let us know what you tried and what worked.
 
Were you able to shoot during those conditions?

I don't spend alot of time in the super cold but do in the hot and occasionally very humid. Mirage so bad a big black circle was hard to even see with high mag scopes.

Impact displacement was still limited to the wind velocity it indicated.

YMMV

Jerry
 
Do a tracking test with your scope on paper at 100yds to make sure it is tracking properly. If it passes then re-attempt shooting at your 500 yd target standing off a tripod (or otherwise elevated off the ground) and see if your results are repeated.
 
Let's assume the OP target at 450yds and 500yds are within a few degrees of arc from the shooting position... if he is shooting one target way over here, then swinging through a big arc to point in a massively different direction, then clarify.

I will continue that he is shooting 2 targets within a small arc... he has confirmed that there is barely any wind... he has confirmed that he is seeing slight movement in the mirage somewhere between him and the target. In either case, wind velocity is very low.... that means the distortion of the image is very small.

If there is consistent and repeatable impacts at 450yds and no where close at 500yds while visually being in a small arc of fire, highly unlikely he is looking through massively different air between the targets.

Why affects from mirage can't be the issue... he has already adjusted for it at 450yds.

Scopes don't always track well and lower grade brands are more prone to having issues... add in the cold and all sorts of things can go wrong

I would do a tracking test and repeat the shooting on another day, elevated if desired... but for me, I would be looking for another optic.

Now if the field has some incredible terrain distortions, that will show up again soon enough.

Jerry
 
Mystic Precision said:
What is your twist rate?

Jerry

In case you are not sure why I would ask... play out your thought on mirage... what is mirage? what does it tell you about the air you are shooting through? what is the MPH range that mirage is visible?

Figure out how fast the air must be moving to displace your bullet a couple of feet over 50yds of flight.

Plan B, got another scope you can try?
Click to expand...
This!:cool:
Cat
 
So I went a week later in warmer weather. Different location, much warmer around -1C. This time the target was up on a hill with a valley between me and the steel, so no possibility for mirage off the snow, only off the barrel. My optic has parallax adjustment so I set it for 500. There was 20 km winds coming in 90 degrees, so it was throwing my shots around 2 feet left of the target sometimes. This time however, I was only around 10 inches high, not 16 inches or more. After accounting for wind and adjusting for height i found the setting on my scope where i finally started making hits. I made 4 consecutive shots on the 500 after moving the scope down by 5 clicks. My latest theory is that I think mirage was only a small factor the first time. The largest factor which I still have to test is what I suspect to be an increase in velocity. My Sig Cross is brand new and I borrowed a chrono to develope my dope after about 150 rounds. I've recently learned that new barrels pick up velocity after break in and now that I've got around 300 rounds down the barrel and I vigorously cleaned it I think my velocity has increased enough that it's in conflict with my dope. I will need to borrow a chronograph again to test this, but if I assume an increase of 100 fps and throw that in a calculator it spits out the same settings I had to use the last time to successfully hit the 500.
 
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