Range Report nonlinear ballistic curve... IE: dope not matching

[Ring]

bullet Hornady 140gr HPBT using a .285 G& BC
scope hight 2.25
Scope = SWFA 5x20 HD
5mil and 10mil [MENTION=18711]BryanLitz[/MENTION] tracking target test done, scope is 100% on
MV from croney at 10ft - 2709fps
average DA here is 1500ft/2500ft

to get my matching dope from 100 to 600y, i need to set MV to 2770 in ANY ballistic calculator.

to get my matching dope from 600 to 800y, i need to set MV to 2740 in ANY ballistic calculator.

i have not had a chance to fine tune it past 800


normaly i would say scope aint tracking, but in this case its 100% dead nuts on

 

[Mod Adahy]

Scopes are never 100%. Nightforce runs 2 or 3 thousandths but that aint your biggest problem. Sounds like you need to run stepped BC's in your program. 900-1000 would be better for velocity truing and then play with stepped BC's to make your dope match. Just my thoughts on it and take it for what it is worth.

 

[CMH]

Have you tried running ballistic calculator with higher BC? 0.290 or 0.295 perhaps?

 

[Ring]

higher BC didn't work, a stepped should, but will need to do some math to figure those out...

 

[Lowlight]

Stepping is the answer, across the board, the problem with an average is, averages don't work at long range very well, or better said, with a lot of different variables.

The short answer is, it's either the bullets, or the barrel, and how that barrel is actually launching the bullet. The way to check it using two chronographs, one at distance and see what is says.

The bullet could be a factor, we just "assume" the bullet is perfect, and we just believe our barrel is "X" (1-8 vs 1-7.8 or 1-8.2)... put the two together and maybe it is deforming the bullet or maybe it isn't spinning like it should hence the bullet is slowing down faster and thus the BC is changing quicker than the computers can account for.

Stepping is where all ballistics calculators should move towards, or the easier solution, have two different tracks in your software.

The problem is, you may change to a different lot of ammo with bullets that are correct and it goes back to working as it should at distance. But I would create two tracks just like you posted.

FYI, new site will have a dedicated ballistic computer section, already added it in

 

[Steel head]

I use those same bullets and Bal AE and a G7 of .285 works quite well for me from 100 to 1090 at home and 100 to 700 at the gun club.
Kinda interesting how sometimes data doesn't jive though.
I have a load with VLD's that's like that.

 

[Ring]

hmmmm if i use the crono speed, of 2705, i need a some REALLY F'ed up BC to jive..

all G7's
300y .32
400y .4
500y .36
570y .33
640y .305



barrel is a 1/8 Kriger on a AIAE 260

 

[Lowlight]

You really haven't said anything...

What does "Jive" mean .. are you .1 off, are you .3 off

and why not try using G1 and see what it does, might work better, a lot of times it does.

In my opinion, anything within .2 is "jiving"

 

[Ring]

my drop chat
100 to 600 done at 2770fps, .285 g7
600+ @ 2705fps

between 610 and 580 is the "gray zone" around 2740fps

Range	Drop
(yd)	(MILS)
100	0
142	0.1
165	0.2
185	0.3
202	0.4
219	0.5
235	0.6
251	0.7
265	0.8
280	0.9
294	1
308	1.1
321	1.2
334	1.3
347	1.4
360	1.5
373	1.6
385	1.7
397	1.8
409	1.9
421	2
433	2.1
444	2.2
456	2.3
467	2.4
478	2.5
489	2.6
500	2.7
511	2.8
521	2.9
532	3
542	3.1
553	3.2
563	3.3

<colgroup><col width="64" style="width:48pt"> <col width="64" style="width:48pt"> </colgroup><tbody>
</tbody>

573	3.4
583	3.5
593	3.6

<colgroup><col width="64" style="width:48pt"><col width="64" style="width:48pt"></colgroup><tbody>
</tbody>

604	3.9
613	4
623	4.1
632	4.2
641	4.3
650	4.4
658	4.5
667	4.6
676	4.7
685	4.8
693	4.9
702	5
710	5.1
718	5.2
727	5.3
735	5.4
743	5.5
751	5.6
759	5.7
767	5.8
775	5.9
783	6

<colgroup><col width="64" span="2" style="width:48pt"> </colgroup><tbody>
</tbody>

 

[Ring]

when i tested to confirm, i ran a target out from 300 to 600 in 50y steps
i was +- .5 to 1" out to 500, 2" max off center at 600 running the numbers above

 

[Lowlight]

Are you kidding,

Like 2" @ 600 from center ... not 2 MOA but 2 Inches ...

You can't dial that, so who cares, what are you shooting that requires 2" accuracy ? If that is the case, get a scope with 1/8th adjustments

 

[damoncali]

duplicate

 

[damoncali]

If you're off even a little at 600, it's a garbage in garbage out problem. Even a non-stepped G1 (assuming it's right) should be pretty much dead on. Screwing around with kludged BCs is going to cause you headaches. Stepped BCs (aka custom drag functions) come into play at long range- well past 600. You should be able to get within 1/4 MOA at 600 without resorting to that.

PS the word you're looking for is "jibe".

 

[Lowlight]

There is far too many variables that the computer can't see and knows nothing about to expect 1/4 MOA accuracy at each yard line, especially with a single "average" number.

Also his scope can only dial .36 so how can you get 1/4 MOA ?

Not to mention the computer nor the shooter can, in real time predict the wind, which can add to small variations in elevation.

1 MOA out of a computer is more than acceptable and anything better is a gift ...

 

[Captain Kirk]

I have ran into the same thing you are describing many times, 243 running DTACs with my ballistic program matching my POI from 100-800 exactly, past 900-1400 yds it was off. Tweak the MV and it causes bigger issues than it solves. I found by tweaking the BC so POI matches my program at the farthest distance I could shoot at the time (1450), it was spot on all the way back in.

Its easy to try, find your actual elevation adjustment needed for a given distance past 800 yds and play with the BC until the #s match, see what happens. Make sure all your atmospheric conditions are as accurate as they can be when you try it, try to use the actual elevation vs pressure.

 

[damoncali]

In my experience *at mid range and shorter* (important qualifier), it's not that hard to get the trajectory to match within roughly 1/4 MOA. you do have to put all of the the relevant numbers in very accurately, but it's doable. Whether or not the scope can get there is another issue. Very roughly speaking, you should be able to get it within a click without resorting to tricks.

 

[Lowlight]

1 Click - .36 x 6 = 2.1" ....

 

[KYpatriot]

What is the ES AND SD of that load? 30 fps of variation is 2 inches at 600 easy. Could be a lot of things if 2 inches is the precision desired. I mean seriously 2 inches of aiming error is easy at 600 yards etc ec.
Not enough data to know, and likely can't hold 2 inch groups at that distance anyway.

 

[Lowlight]

Great graphic used at Gunsite

Top of the group, center of the group, bottom of the group... where is your group center ?

Even If you are a 1/2 MOA shooter at distance, the variation could easily be 1 MOA unless you determine the center of the group.

How many shots determined the POI and how big was the group in that determination ?

 

[Ring]

not saying i want to be dead on to the inch, just saying the drop listed for 2770 matched what i saw in the field out to 600, at 620 + it matched data 2740

normaly what i do is at 1k ill use a small target, say a clay pigeon.. i will dial till im hitting or within a 6" radius of it and use that # as my dope to true.

i normaly do this on zero wind days, or light 1-3mph wind days

 

[KYpatriot]

Ok so maybe the one shot actually was 2770 and the other 2740. That, or aiming error, inherent dispersion, or LL points out determining true group center, etc etc

 

[Ring]

the day i did it, i ran all shots over the crono, if i had i high vertical miss, i looked at the crono to see if the FPS was off the norm, if it was, i ignored that shot

 

[KYpatriot]

So what velocity variance are you accepting? Are you recalculating the drop with the app after measuring with the chrony, and then comparing the number it gives with what was actually required at the target? Is your purpose to verify the accuracy of the app? You will need a very precise rifle/shooter combo to do this, even then it would be sketchy to blame the app with much confidence unless everything else is near perfect. How confident are you with aiming error? Any mirage at all? Headwind/tailwind? Is your zero exactly zero or is a group fired at zero range really a quarter inch high or low as is very common, especially with mil/mil scopes? I appreciate what you are trying to do but you have to lock down a lot of variables before you can blame the app with any honesty/confidence.

For example, if your zero is .25 inch high, which is less than a click at 100 yards, the true zero range is about about 70 yards and your dope will be about 2 inches off at 800 yards. So if you have a scope with 1/10 mil clicks you may need to get your zero as close as possible then run the numbers in the app with your TRUE zero range not just putting in 100 because that's the distance you tried to zero your rifle.