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Range Report Balistic Cards don't match DOPE at Long Range

F

footman2000

Private
Minuteman
Nov 27, 2009
27
0
52
Colorado
I created a density altitude range card on the JBM website and went out to the range to check the card vs. real shooting. The rifle is a 6-250 shooting ~.3MOA groups.

Ammo win brass, IMR 4350 37.5gr, Hornady Match 105gr, CCI BR2, flying 2950fps with a standard deviation of 9.

Rifle Remington action blue printed with a Rocky Mountain Rifle works barrel, Sightron 8-32 LR SIII scope sitting 2.0" above the center line of the barrel and a 10MOA base.

Range conditions were Density altitude of ~5500-6000ft, 54F, minimal wind.

at 200yds money
at 300yds money group .3MOA
at 500yds .25 MOA above the card group .5MOA
at 600yds .5 MOA above the card group .3MOA
at 800yds 1.5 MOA above the card group .5MOA
at 900yds 2.25MOA above the card group .5MOA
at 1000yds 1.25 MOA above the card (breezes were a little shifty and patterns were not as consistant therefore less reliable in my opinion.)

Is this a result of the MOA base? I have been playing with the numbers BC, Velocity, etc with little help at getting a real close result. Any help would be appreciated.
 
Re: Balistic Cards don't match DOPE at Long Range

It's not a result of the base you're using.

It could be that the card you ran in JBM is just a little bit different than the actual conditions in the ATM or velocity, or BC.

At 1k being off by about 12" is reasonable for a couple little changes such as being off by a few degrees in temp, a few FPS in velocity, and a few points in BC.

If all of those things check out, when was the last time you checked your scope's travel at 100yd on a grid to make sure that what you THINK you're dialing up is what you're actually getting in the scope's erector?
 
Re: Balistic Cards don't match DOPE at Long Range

I am getting pretty close with a BC of. 595. This is actually within .5 moa a cross the board. I made a mistake in my on the 800 and 900 yd readings. Each was decreased by 1 moa. 15moa / revolution of the dial not 14.
 
Re: Balistic Cards don't match DOPE at Long Range

.595 sounds way high. If it is that good, that is one heck of bullet.
I'd check your scope as Bohem suggests and then redo the test, or not sweat it beyond noting in your data books the adjusted comeups.
 
Re: Balistic Cards don't match DOPE at Long Range

I know it is high on the Bc, but it is working. The velocities I got were really consistent and it was the same temp. I didn't really know if I should change the BC or the velocity. I seem to run into this when I go to the range and test dope vs balistic calculations. I have 1000 to 10000 in 3000ft increments for density altitude, none of them fit. I guess that is why we go to range and verify with dope. Does anyone have perfect cards from the get go?
 
Re: Balistic Cards don't match DOPE at Long Range

I know it is high on the Bc, but it is working. The velocities I got were really consistent and it was the same temp. I didn't really know if I should change the BC or the velocity. I seem to run into this when I go to the range and test dope vs balistic calculations. I have 1000 to 10000 in 3000ft increments for density altitude, none of them fit. I guess that is why we go to range and verify with dope. Does anyone have perfect cards from the get go?
 
Re: Balistic Cards don't match DOPE at Long Range

I make my cards up in 2K increments. There is not much difference in the numbers until you hit the ranges where you were seeing issues. I'm inclined to believe 3k increments may be too much. Did you check the numbers you were getting against the actual "real time" DA?
 
Re: Balistic Cards don't match DOPE at Long Range

Yes, I did look at the real time DA which was between 5500ft and 6000ft on average cross reference with a temp of 55F.
 
Re: Balistic Cards don't match DOPE at Long Range

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: footman2000</div><div class="ubbcode-body">I know it is high on the Bc, but it is working. The velocities I got were really consistent and it was the same temp. I didn't really know if I should change the BC or the velocity. I seem to run into this when I go to the range and test dope vs balistic calculations. I have 1000 to 10000 in 3000ft increments for density altitude, none of them fit. I guess that is why we go to range and verify with dope. Does anyone have perfect cards from the get go? </div></div>

Using Shooter I gathered dope out to 950 , backed into velocity. With these numbers I made cards with 1k increments, every card so far has been within .1. Dope was collected at 3500 da, shooting today in -200.

I prefer to back into my velocity rather then use a chronos. I have had much better results.
 
Re: Balistic Cards don't match DOPE at Long Range

That BC is way too high. Have you ever ran a tracking test on the scope to make sure it's tracking correctly? If you have good chrono numbers and put your correct data in JBM then it should be pretty close. I have never been off more than .2 mils at 1000.

What was your altitude? Actual, not DA?

Also what was your JBM data for those ranges?
 
Re: Balistic Cards don't match DOPE at Long Range

One thing that occurred to me from the gentleman who spoke of the scope. It appears I am at the end of the adjustments. The scope has always been on but it is a 70 moa scope and I am at 35 up. I have a hunch that is not good.
 
Re: Balistic Cards don't match DOPE at Long Range

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: footman2000</div><div class="ubbcode-body">One thing that occurred to me from the gentleman who spoke of the scope. It appears I am at the end of the adjustments. The scope has always been on but it is a 70 moa scope and I am at 35 up. I have a hunch that is not good. </div></div>

That is very telling actually. A lot of otherwise "true" scopes have issues at the extremes of the adjustment range. Especially since you're consistenly within 1/2 MOA and then over the last few minutes of adjustment it falls off quickly.

I would suggest that you put a base on there with more inclination built into it, right now you probably have a 10 or 20 MOA base on there, try a 30.

Also, run the EXACT conditions that you were shooting in through JBM once you replace the base and see if you get much closer. My experience with my Vortex Razors and previously my Nightforce NXS series scopes is that they were within +/- 1/4MOA of the JBM information when the data inputs to JBM were closely tracked.
 
Re: Balistic Cards don't match DOPE at Long Range

I just don't think that weaver base is a true 10 map base. I just put on a 20 moa base. Back to the range when the snow melts. I bet this will let me get back to a more reasonable BC.

Knight thanks for that input on backing into the velocity. I will be trying that in the future.
 
Re: Balistic Cards don't match DOPE at Long Range

I put trust in my Oehler and JBM to get me to a starting point from which I develop my dope by shooting KD targets. When I get my inital JBM trajectory poop I compare it to what my actual shot elevations are at the distances. Generally I can add or subtract fps and get match it to the actual elevations across the range and come up with a good dope card. This tells me that either the chrono might have been acting up just a little, if I didn't enter something right on JBM, etc.

Sometimes I forget to put in 15' to the chrono instead of the default which will mess with your mind LOLOL.
 
Re: Balistic Cards don't match DOPE at Long Range

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">You might find this a useful explanation of some reasons why the program output does not match your field results:

Sources of Inaccuracies in Ballistic Programs

</div></div>

I had similar differences in my original DA ballistic cards, I followed Lindy's advice on his website by adjusting the MV until the card read what my round was doing. It worked great. As long as you take good notes at the range you can get the numbers right on the computer pretty easily.

Thanks Lindy
 
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