Range Report 1000 yd day...elevation off

[lennyo3034]

I went to 1k today and am trying to figure why my drop was so far off what my ballistic calculators were outputting.

I get to shoot at 600-700 yards a dozen or so times a year, but this is only my second trip to 1000 this year.

I brought 3 rifles, 2 were off significantly, 1 was pretty close. All shot very accurately, the elevation being off is what's concerning.

Conditions:
Peacemaker National Training Center: 746 ft Altitude
2900-3100 ft DA
87 degrees
30% humidity
Bright and sunny, significant mirage

Wind today was blowing in various directions but was not heavy. Only 1.4 mils max wind needed today. Windage was not a concern. Some did mention they thought there was a thermal occurring.

The results:
7mm Remington Mag
180 Hornady ELD @3066
Ballistic computers: 5.6-5.7 mils
Actual drop: 6.1 mils
Steiner M5xi 5-25, Tall target to 10 mils completed and passed this week

6.5 Creedmoor
139 Lapua Scenar @ 2800
Ballistic computers: 7.9 mils
Actual drop: 8.6 mils
Gen II Razor, Tall target to 10 mils passed last year

.223 Remington
80 Hornady ELD @ 2820
Ballistic computers: 8.9mils
Actual drop: 8.7 mils
Steiner T5xi (upgraded turrets), Tall target test not done

All zeros and velocities were confirmed today. Velocities have been measured using two different magnetospeeds and a shooting chrony. All were within 10 fps. I verified again with the magnetospeed at the range today with a few rounds from each gun after noticing dope off.

My previous trip to this range, I only had the 6.5 creedmoor. It was colder and there was a much lower DA. My output from shooter was dead on with 8.7 mils.

I was using Shooter and Strelok pro, both of which were pretty close.

Is there a factor I'm missing? I also found it interesting that the .223 actually required less drop than calculated and was only .1mil off from 6.5 creedmoor.

 

[Killswitch Engage]

mirage brother. the error is about exactly what is seen in heavy mirage conditions. for sure....

 

[lennyo3034]

mirage brother. the error is about exactly what is seen in heavy mirage conditions. for sure....

I've given extra elevation in the past (lights up sights up) due to heavy mirage. Is there a way to quantify it?

 

[Sheldon N]

I've watched most of our squad miss a KYL rack at 300 yards 0.2 mil low. Range on the target was solid, no real wind to speak of. We were shooting prone and the ground actually rose up a tiny bit before dropping away 5 feet. You were right on the ground and the foreground was up high enough that the grass horizon line was at the bottom edge of the target. You couldn't see the misses underneath and the mirage was really bad.

I actually missed the big target first shot completely, scratched my head and shot again at the second largest target... missed again. Assumed I had to be missing low since I couldn't see it, dialed up 2 clicks then went 7/8 on the rest.

Amazing how much effect the mirage can have even up close like that. Watched shooter after shooter send shots directly underneath each of the plates.

 

[tnichols]

Explain this to me. Doesn't the mirage "lift" the target i.e. the image appears higher than the actual target itself, thus, impacts would be high? I've heard the suns up sights up more than once, so I have no doubt that that theory is sound.

 

[lennyo3034]

I went and verified zero and did a tall target test on all three yesterday. The zero on the .223 was off by .1 mil. The other two were dead on. All three passed the tall target test with flying colors.

Looks like mirage was indeed the culprit.

Interestingly, if I used absolute pressure instead of DA, shooter gave me a dope much closer to my actual drop.

 

[Killswitch Engage]

go back on a overcast day or first thing in the am and shoot it. i guarantee you'll see different results. on my personal range when the mirage kicks in at 700-1k you're .3-.4 low as sure as can be.

 

[tnichols]

go back on a overcast day or first thing in the am and shoot it. i guarantee you'll see different results. on my personal range when the mirage kicks in at 700-1k you're .3-.4 low as sure as can be.

I agree. Shot yesterday with an overcast and today in bright sun. Mirage was flat due to wind. All other atmospherics nearly identical and ballistic calc calling for the same elevation. I was 0.1 low at 1065 compared to yesterday's impacts. Just having a hard time wrapping my mind around the cause or the why.

 

[lennyo3034]

Its almost impossible to troubleshoot these common questions from a distance. Your actual drop and BC calculated drop are meaningless without the DA, at least, attached to those numbers. Additionally, you said you held 1.4mrad for wind? with a 180ELDM @ 3066 or the 223? If 7mm, what does that make the wind speed? 14mph? If so you have crosswind jump effecting your data by at least .1. Also sounds like you might not have the atmosphere correctly configured. Sounds like you could have a mix of compounding errors. BC's are also not consistent from gun to gun. I would make sure all the inputs are correctly configured and then simply true my BC based on actual drop. Lot's of folks true with a shot or two on target. Go to a 1000yd Fclass match and get a good 20 - 60rd aggregate of data points over the course of a day and three shooting positions. I would trust that.

I had the DA listed in the OP. The 1.4 mil wind hold was with the .223 when the wind was gusting.

You're probably right about not having atmosphere correctly configured. What do I have to do in order to do so? I was using a kestrel 4500 and the DA matched another's.

Miragr certainly could have been a factor, although it doesn't explain why the .223 needed LESS drop than calculated.