300 Yard Group Off by 2 Inches

[DSPrecision]

I went to the range today and did some shooting at 300 yards. My Kestrel was calling for 1.1 mils of elevation but I was hitting .2 mil low. Ie: I actually needed 1.3 mils. I’m using a custom drag model, lab radar, and am getting SD’s below 10 and ES below 20. Zero at 100 yards is dead on and at both ranges I’m able to shoot .3-.5 MOA 5-shot groups consistently. Any ideas why I was impacting ~2” low?

 

[acudaowner]

my first guess is always going to be the shooter but if you give your gun a good once over and everything else is spot on then Id go back and say it's most likely the shooter but that's my opinion ( totally worthless) but it's mine .

 

[CoryT]

How was the drag model created? Had it been verified in some way prior to this?

 

[DSPrecision]

It’s the AB custom drag curve for the 140 ELDM.

 

[Statusquo]

Did you have a lot of boiling mirage?

 

[DSPrecision]

my first guess is always going to be the shooter but if you give your gun a good once over and everything else is spot on then Id go back and say it's most likely the shooter but that's my opinion ( totally worthless) but it's mine .

700 rounds through the gun and every group is sub .5 MOA. I’m not great with wind, but I can shoot a good group. Everything is torqued to spec. Etc. Indoors at 100 is spot on.

 

[DSPrecision]

Did you have a lot of boiling mirage?

Yes. It was 95° and winds were 2-4 mph. from 6:00-9:00 through the day. All six, five-shot groups were low. Rifle is zeroed at 100 yards indoors at 75°.

 

[ma smith]

maybe check your speed ?

 

[Statusquo]

Yes. It was 95° and winds were 2-4 mph. from 6:00-9:00 through the day. All six, five-shot groups were low. Rifle is zeroed at 100 yards indoors at 75°.

Assuming your scope tracks true, speed and dope are good, I would chalk it up to mirage.

 

[pell1203]

In this case, wouldn’t mirage and winds have him hitting higher and slightly right?

 

[Statusquo]

In this case, wouldn’t mirage and winds have him hitting higher and slightly right?

Yup, apparently I can’t read good

 

[6.5SH]

OP, without providing the rest of the info (Velocity, sight height, environmentals) it is impossible to do anything more than guess.
Have you shot that distance with the same conditions and your prior calculation was 1.1 and a successful impact?

The CDM are not the same as a PDM, so unless you have trued it up it's likely wrong.
Just hazarding a guess of 2700 fps, 1.5" sight height and a DA of 4000, I get 1.1 mils with AB's G7 of .291 (not even their CDM).
Using the older Litz engine in Shooter with a banded G7 using Hornady's values of .326/.320/.310 I get 1.3 mils with the rest of that data.

 

[seansmd]

OP, without providing the rest of the info (Velocity, sight height, environmentals) it is impossible to do anything more than guess.
Have you shot that distance with the same conditions and your prior calculation was 1.1 and a successful impact?

The CDM are not the same as a PDM, so unless you have trued it up it's likely wrong.
Just hazarding a guess of 2700 fps, 1.5" sight height and a DA of 4000, I get 1.1 mils with AB's G7 of .291 (not even their CDM).
Using the older Litz engine in Shooter with a banded G7 using Hornady's values of .326/.320/.310 I get 1.3 mils with the rest of that data.

Good advice here need to true mv.

 

[DSPrecision]

OP, without providing the rest of the info (Velocity, sight height, environmentals) it is impossible to do anything more than guess.
Have you shot that distance with the same conditions and your prior calculation was 1.1 and a successful impact?

The CDM are not the same as a PDM, so unless you have trued it up it's likely wrong.
Just hazarding a guess of 2700 fps, 1.5" sight height and a DA of 4000, I get 1.1 mils with AB's G7 of .291 (not even their CDM).
Using the older Litz engine in Shooter with a banded G7 using Hornady's values of .326/.320/.310 I get 1.3 mils with the rest of that data.

2680 fps at 80°, 2.58” bore height, wind 2-4 mph @ 10:00, Hornady 140 ELDM custom curve from bullet library on a 5700 Elite. I’m in Colorado Springs, and it was 95° so DA was probably around 8,500’.

Shooting an AT-X and NF 7-35

 

[DSPrecision]

I’ve shot from 400-1,000 with good, predictable results.

 

[6.5SH]

I’ve shot from 400-1,000 with good, predictable results.

So if the calculations have proved accurate before and nothing was changed or fat fingered, what was the lighting like?

Excellent video example of just how weird things can get:

 

[Kestrel Ballistics]

I went to the range today and did some shooting at 300 yards. My Kestrel was calling for 1.1 mils of elevation but I was hitting .2 mil low. Ie: I actually needed 1.3 mils. I’m using a custom drag model, lab radar, and am getting SD’s below 10 and ES below 20. Zero at 100 yards is dead on and at both ranges I’m able to shoot .3-.5 MOA 5-shot groups consistently. Any ideas why I was impacting ~2” low?

If error is consistent, do Cal MV function to true the Kestrel to your rifle.