Drop data really off, based on zero

[cmorsch]

Im having trouble understanding what happened with my drop data. I was shooting my 300 Ultra Mag and verified my zero at 100 yards, then went to shoot at 1000 yards, and I needed a extra .5mils of elevation to get to 1k over what my ballistics info said based on my muzzle velocity. Would the fact that I was shooting sitting with a bipod on a concrete bench at 100 and laying prone on the ground at 1000 effect my point of impact that much? And also can I rezero my rifle at 100 by backing down the number of clicks that are indicated in the drop data in my applied ballistics app, and reset my turrets?

 

[406precision]

I would zero from the prone position.

 

[Barrelnut]

Sometimes you have to adjust the published BC value for the bullet you are using so the app will match what your rifle/bullet combo shoots. In this case try using a lower value until your app produces the correct number of MOA to dial. The verify at other ranges.

 

[gohring3006]

Sometimes you have to adjust the published BC value for the bullet you are using so the app will match what your rifle/bullet combo shoots. In this case try using a lower value until your app produces the correct number of MOA to dial. The verify at other ranges.

This pretty much sums it up

 

[cmorsch]

Incase it matters I am shooting the Berger 230gr Hybrid Target, and am using the custom ballistics curve in the applied ballistics program.

 

[Barrelnut]

Incase it matters I am shooting the Berger 230gr Hybrid Target, and am using the custom ballistics curve in the applied ballistics program.

I use the Berger VLD 210 for 30 cal and the 140 VLD for 6.5 cal. and I have to make some adjustments for both of them. It may also be possible that your scope is not accurately dialing the MOA values, this happens.

 

[WildRose]

What scope are you using? It is possible that it's not accurate in click values.

As others mentioned above though the most likely cause is related to BC and velocity. You can tweak your velocity and BC in your program until it gives you answers that match up to your real world drops on paper.

This is why many of us suggest verifying your drops at, at least three different ranges and adjusting the inputs to your ballistics program until the outputs are as close as possible to your real world results.

If you can get it right at three different ranges then it should be right across the entire scale.

 

[7magcreedmoor]

Questions to answer:

1 Is the drop data you were using verified or raw?
2 Have you previously tested the scope's tracking accuracy?
3 Have you previously tested the rig's point of impact consistency from different firing postions/rests?

If you shoot with a bag type rest from the shooting bench but use a bipod for prone, it is not unusual to find a point of impact shift between the two. Resting the fore end on a backpack can provide just enough give to simulate the sandbag from the bench, whereas metal bipod legs on hard ground change the way the rifle moves during the recoil impulse. If you plan on shooting with the bipod in the field, use it to zero as well. Apples and apples, as it were...

 

[cmorsch]

The scope is a vortex viper PST that I took off another rifle and does track correctly. It is raw data at 1k, but the base velocity was measured by a chronograph averaged 2965. When I ran the ballistic calibration in the ballistics program it was saying that my velocity was in the mid 2700's. which isn't close to what the chrono was telling me.

 

[Barrelnut]

Which ballistics program?

 

[cmorsch]

Applied Ballistics for the android.

 

[RockyMtnMT]

I would like to see you back it down to zero based on the calculations and see where your zero hits. A small error at 100 is a big error at 1000.

Also check Scope height.

Steve