Range Report Can someone explain?

[SnkBit]

I'm shooting my .308 with 175smk's over 44gr of varget averaging 2686fps. We are shooting at 3094' altitude in 80* temps with 29.44" pressure and 10% humidity.

JBM calls for 13.7moa of elevation @ 575yds. I am dialing 11.8moa to hit target. I'm using JBM to calculate the trajectory for my -06 as well and it is very close for that gun.

What is happening on the .308? Am I missing something?

 

[KNIGHT11B4]

Re: Can someone explain?

Ensure that you have all of the input data correct when using any BC program such as JBM.

What about at other ranges? Is JBM giving you correct or close to correct answers there?

Are you shooting the -06 at the same targets? Could angle be an issue?

Oh and the often overlooked but commonly the cause... Have you box tested both optics to see if they are tracking correctly?

 

[SnkBit]

Re: Can someone explain?

Shooting both rifles at same targets.

Haven't had the opportunity to shoot at other ranges as of yet.

I was thinking the same thing on the optics. Both scopes are the same but they are fairly cheap Konus scopes. I will box test the scopes and see what I get. Although, it seems to track well when making adjustments.

 

[KNIGHT11B4]

Re: Can someone explain?

I would box test both, call me crazy, but I do this on every optic I receive.

Testing at other ranges (meaning distance) will give you a better understanding as to what is truly happening. You may find that you need to adjust your MV and/or projo bc to get JBM closer.

FWIW, nothing beats DOPE.

 

[BigMahi]

Re: Can someone explain?

Make sure you measure your scope height and input it correctly. Do a search on how to measure distance between bore center and scope center, then click on the (?) next to the Sight Height / Zero Height.

 

[BigMahi]

Re: Can someone explain?

Here you go:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1433025#Post1433025

 

[SnkBit]

Re: Can someone explain?

Scope height is correct, not to mention it may be changed in the JBM calc's with little effect.

 

[AKAce]

Re: Can someone explain?

Target is not at the range you think it is.

IPHY VS true MOA

Scope Adjustments not just right.

Are you using the Litz BC ? (You Should)

 

[ida83704]

Re: Can someone explain?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SnkBit</div><div class="ubbcode-body"> We are shooting at 3094' altitude in 80* temps with 29.44" pressure and 10% humidity.
Am I missing something? </div></div>

Yes, there is no way you are at 3094 feet and have a baro of 29.44.

29.44 is pressure corrected, you need to sort out the diff between corrected and uncorrected pressure.

 

[SnkBit]

Re: Can someone explain?

Target distance has been checked multiple times with various range finders.

I am using the Litz numbers.

The pressure is corrected station pressure and is being entered as such in the JBM program.

I'm really leaning toward the optics at this point.

 

[notquiteright]

Re: Can someone explain?

How did you calculate you were using 11.8MOA? My scope can do 11.75 and 12.

 

[Trevor]

Re: Can someone explain?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SnkBit</div><div class="ubbcode-body"> We are shooting at 3094' altitude in 80* temps with 29.44" pressure and 10% humidity.
Am I missing something? </div></div>

Yes, there is no way you are at 3094 feet and have a baro of 29.44.

29.44 is pressure corrected, you need to sort out the diff between corrected and uncorrected pressure. </div></div>

agreed a quick check of station pressure put you closer to 26.8 range you may wish to imput that data and see what you get.

Trevor

 

[SnkBit]

Re: Can someone explain?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: notquiteright</div><div class="ubbcode-body">How did you calculate you were using 11.8MOA? My scope can do 11.75 and 12. </div></div>

My scopes turrets are .125moa. Technically I had 11.875moa dialed.

 

[SnkBit]

Re: Can someone explain?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Trevor</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SnkBit</div><div class="ubbcode-body"> We are shooting at 3094' altitude in 80* temps with 29.44" pressure and 10% humidity.
Am I missing something? </div></div>

Yes, there is no way you are at 3094 feet and have a baro of 29.44.

29.44 is pressure corrected, you need to sort out the diff between corrected and uncorrected pressure. </div></div>



agreed a quick check of station pressure put you closer to 26.8 range you may wish to imput that data and see what you get.

Trevor </div></div>

The best that does is 13.0moa, still not nearly enough to account for the 11.8 dialed.

 

[exhogflyer]

Re: Can someone explain?

Try another chronograph

 

[SnkBit]

Re: Can someone explain?

I'll double check it against another chrono and see what I get.

 

[jbmillard]

Re: Can someone explain?

At what conditions did you establish zero? Have you read this: Elevation?

Brad

 

[SnkBit]

Re: Can someone explain?

While that is a very useful trick that I did not know how to use prior to your post, it doesn't even get me close. I'm going to check the optic and double check the chrono to see if there is any misrepresentation there before I get too worked up about it. I actually sold the rifle to a friend and swapped the optic to a rimfire so I will have to go about it a little differently I suppose.