Ballistic question - I am stumped

[M Jager]

Playing with 150 PVA Cayuga in my factory tikka 7mm mag.
Claimed BC .311 G7. Cody Adam's trued his to .300ish G7

Velocity 3150 (lab radar and magnetospeed confirmed.)
Sight in 2moa high at 100, confirmed zero at 255 yards.
Elevation 3365, pressure 26.45, humidity 50, temp 65. (Kestral verified and also consistent with previous shooting at this location.
Predicted drops (shooter and hornady)
400 - 2.75 moa
600 - 7.25 moa
1k - 18.75 moa

Actual drops
400 - 3.25 moa
600 - 9.25 moa
1k - 20.75

To get drops to match at 600 I have to drop the DC or velocity ridiculous amounts, which predictably puts it way off at 1k. Checked tracking on the scope and it's spot on. After checking tracking, I shot again at 100, 255, 400, and 600 with the same results.

Any ideas would be appreciated and I am out of them.

 

[wasskeet]

How plumb is the bench to target at your range?

 

[Creedmoor shooter]

This bullet is a mono correct? What is the recommended twist rate for it? It could be its not fully stabilizing and getting the full BC out of the bullet

 

[M Jager]

How plumb is the bench to target at your range?

Shooting prone, pretty flat in both locations I tried.

 

[M Jager]

This bullet is a mono correct? What is the recommended twist rate for it? It could be its not fully stabilizing and getting the full BC out of the bullet

PVA calls for a 9 and I am running a 9.25 at 3300' altitude so I should be good. Even if we are are degrading slightly, we at talking of going from .3ish g7 to sub .19 g7 to line up at 600.

 

[Mikecr]

What conditions was the .311G7 determined with? ICAO? StdMetro, StdArtillery? Local?
Are you entering altitude, or Abs/station pressure, or SL adjusted pressure, or a combination altitude/pressure?

 

[StanleyActual]

So you're truimg your velocity out to 600 and then truing your BC past that correct?

 

[dfanonymous]

If he verified with kestrel then it already uses the correct atmospherics. No need to confuse anyone about station pressure or density of air.

More about that in a second.

BC won't have a extreme effect from the off the box. Not at 600. Maybe at 1k but that around 1 moa most between .300 and .311 at 1k.

The problem more than likely lies in the weird system the OP is using with 2 inch high @ 100 but zero'd at 255 and the the data input into the system. Another problem could be using hornady app? If that's the case, and I could be wrong, but I'm pretty sure they only use hornady bullets…which inherently use hornady bullet form factors.

However, to revisit the atmospherics, I don't think you can have a station pressure of 26.45 in that temp at that altitude unless you were shooting in the eye of a major storm…

My logic based on a simple DA chart as admittedly I'm not a meteorologist.

 

[Maol]

What other bullets have you tried and how did they work?

 

[martinakl]

I had a similar experience awhile back. One suggestion that stuck with me is it's better zero at 100 yards.

 

[StanleyActual]

If he verified with kestrel then it already uses the correct atmospherics. No need to confuse anyone about station pressure or density of air. More about that in a second.

BC won't have a extreme effect from the off the box. Not at 600. Maybe at 1k but that around 1 moa most between .300 and .311 at 1k.

The problem more than likely lies in the weird system the OP is using with 2 inch high @ 100 but zero'd at 255 and the the data imputed into the system. Another problem could be using hornady app? If that's the case, I could be wrong but I'm pretty sure they only use hornady bullets…which inherently use hornady bullet form factors.

However, to revisit the atmospherics, I don't think you can have a station pressure of 26.45 in that temp at that altitude unless you were shooting in the eye of a major storm…

My logic based on a simple DA chart as admittedly I'm not a meteorologist.
View attachment 295853

yep, I'm trying to see if I can generate his results running it through my AB software and it's way off. I agree, the issue maybe with the 255 yd zero deal and that station pressure.

 

[Maol]

Scope height matters too. He didn't mention it. Hornady's app uses 1.5 unless you change it. Zero doesn't matter just enter it. Hornady's app will take all the data he gave including the crazy low pressure.

 

[dfanonymous]

Scope height matters too. He didn't mention it. Hornady's app uses 1.5 unless you change it. Zero doesn't matter just enter it. Hornady's app will take all the data he gave including the crazy low pressure.

Zero matters if you think you're good at 255 and you're not.

It also matters if you're you left it at 100y and it's at 255.

It also matters because these dumb 200+ yard zeros are effected by atmosphere more than a 100y zero. Any errors built in your zero are built into your shot. Then you come onto a forum wondering where you dun ****'ed up at.

 

[StanleyActual]

It also matters because these dumb 200+ yard zeros are effected by atmosphere more than a 100y zero. Any errors built in your zero are built into your shot. Then you come onto a forum wondering where you dun ****'ed up at.

X2
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