Problem with any ballistics calc or am I just 'special'?

[OGinMi]

I have an issue with back calculating bullet ballistics using several calculators (Applied Ballistics, Strelok, BallisticsARC, JMB Ballistics, Hornady 4DOF) from the DOPE I recently got.

Looking for some expert advice here but please be patient with me. My situation might be unique.

Let me start with the hardware:
1. .308 barrel, 24" long, 1:10 twist, muzzle brake
2. Hornady factory ELD Match ammo, 168gr bullet. Advertised BC of 0.523. Chrono'd with MagentoSpeed Sporter at 2668fps (70degF, 45% humidity, 28.91inHg, DA 1994ft). Pretty close to the specs on the box.
3. Sight height from bore: 2.375"

Weather:
32degF, press 28inHg, humidity 40%, DA 13 ft (yes, that low)
There was an average wind of 15MPH that day at 3 o'clock (but that shouldn't factor into the issue very much).

I got the chance to shoot a session at the ONLY long range in Michigan where I live. KD targets out to 1050yd. It's a hike and exclusive so I can't get there but a couple times per year for matches and no practice. So I used this chance to get some DOPE to take back and tweak the elevation marks I got from several ballistics calculators online and get a range card I could trust as a baseline for matches.

So I take the initial sight marks (come up, elevations, whatever u want to call them) and we are ok out to 675 yds, a little low given the weather but not a huge issue.

Then I try shooting the 1050 yard target. Bullet splash 50 yards IN FRONT of the target. After taking another 10 rounds and walking the shot to the target, the result is WAY off any calculator estimate.

Here's a twist that I hope won't lose folks from helping out. I use MOA.

So here goes the data download:
Almost any ballistics calculator tells me around 34MOA to get 1050yds at 70 degF.
Adjusting for conditions that day and sight scale factor with Applied Ballistics solver, I get a solution of at 44MOA.
The actual dial up was 53MOA! Verified with several shots.

It seems this combo of barrel and bullet results in a curve that goes exponential after 700yds. Well that ain't right I'm thinking.

So adjust the single BC in each calculator to tweak it closer to the 1050yd dial-up I got. Not surprising, as I lower the BC (down to 0.476, which might average out the high/med/low speed BC), the further away from shorter range DOPE recorded at the range that day. For those that are interested I attached a graph of the data with specs in the legend.

So my question is, what ballistics calculator with the right variables would help me with matching this actual DOPE data? Or what variable am I not accounting for?I can'r run out to the range and fingerprint this barrel every 25 yards under various conditions and need a ballistics calc that can help estimate elevations more accurately than the ones mentioned above.

Any advice is appreciated (aside from don't shoot a 308 for longer ranges).

 

[CoryT]

This seems like a scope issue, has this scope been calibrated across full travel?

 

[Long Range 338]

#1 always believe the bullet. In this case it really sounds like a scope tracking issue and your error is compounding at distance. Have you tested the scope?

 

[stello1001]

tracking test!!!

 

[OGinMi]

Good points. I did a tracking test a couple times but only went up 24MOA rather than the full scale 60MOA. For the tests I did, it showed consistently a linear +3% error. I took that into account with Applied Ballistics calc using their 'sight scale factor' still WAY off at long distances.

I will try to find a way to do a full scale tracking test and see if it goes non-linear and can explain the results out at 1000 yards.

IF that is the case, how do I account for a non-linear scale factor? Applied Ballistics only has a single value so it assumes it is linear. Any suggested calculators that give 'trueing' at multiple points to capture a non-linear scope?

Thanks for all the good feedback!

 

[CoryT]

If it does not track, return or replace the scope. It seems like you have an issue where the internals are either bumping up against the outer tube or overcompressing the springs, limiting travel. It's possible that may be fixed with more slope in the base, then again, perhaps not. Were you by chance also getting some windage issues as you increased the range?

 

[Lowlight]

The Rifle System cannot be matched to the computer, you have to match the computer to the rifle system.

That means you have to actually dope the rifle first and then align the software to those values under those conditions. Once that is done you can then use the computer to predict a solution. It's a process not a shortcut.

Every ballistic calculator on its base level is doing the exact same thing, the real variations are two-fold, 1.) 3DOF vs 4DOF which adds in Pitch and Yaw, and 2.) Publisher Liberties to align things like SD and CE when the calculator does not have the inherent means do it on its own. So 3DOF vs 4DOF doing the same thing.

They are equally accurate given the correct variables to use. There are no free rides, the shooter has to do their part.

The benefit of a computer is the change in conditions that fall outside of the information found in one's databook. In other words, rather than shoot a host of conditions and record the results, (Data On Previous Engagements) we can shoot one set of conditions, record the data, and then after aligning that information to the computer, the computer should be able to predict the solution under varying conditions.

 

[OGinMi]

CoryT, good point. I have done the circle tracking (up, right, down, left) with this scope a couple times. Aside from the 3% error (within the 24MOA range I mention), it returns every time to the origin so I don't think it has some random tracking or losing zero issue. And I have not found any windage creep in the zero or elevating up/down through several trials.

lowlight, totally understand your point. In my past experience with long range target archery (100+ yards), I would use the same approach as I am doing now. Get some real world marks and then use a calculator to 'tweak' variables to match up the sight marks. This allowed me to interpolate to points I didn't get real data for. I'm trying the same here but there are so few variables to 'tweak' in the calculators I have found that I end up with huge errors at one end or the other. Which is why I posed the question here. Is there something I am missing or is there a calculator with more variables that would help me 'tweak' the calc to match the rifle (not the other way around)?

Appreciate all the help.

 

[Lowlight]

I would adjust MV at 600 yards and then adjust BC at or after 800 yards to true your data, this process tends to balance the curve better.

Shooting to 1050 yards nothing should be way off, the trajectory is still pretty consistent. So there have to be input errors or scope tracking issues but even then, unless the scope is way off, you might see, maybe .5 mils of variation at 1000, usually it grows with range.

I would start off by:

1. Confirm atmospheric variables,
2. Dope the rifle to distance recording as many yard lines as possible, sans software.

Then go about inputting everything into the computer at your desk vs on the range. After this, you can go out and confirm it. Doing this the variations should be rather small. If you are more than 1MOA off in elevation I would suspect an input error or tracking issue. But nothing should be "way" off with any software today.

We have tons of data, tons of people doing this every day, stuff should not be way off if you are adding in all the variables correctly. And Personally I don't think the answer is to add more variables to adjust, in fact, I would say turn off most of them that you can. Use the basic data

I bet if you posted your dope as noted above, give us the conditions and the data, even if you just gave us 300, 600, 800, 1050, we can probably build a JBM Card in 30 seconds that would be right. If it's not, it will probably point out the issue.

 

[OGinMi]

lowlight, thanks for the feedback. I'm wondering if we are talking about using a different JBM calculator. I have use this one:

JBM - Calculations - Trajectory (Simplified)

www.jbmballistics.com

Attached are the results using that tool with the correct environmental and bullet BC info. Again, beyond 600 yds, the calc deviates badly from the DOPE.

You mention adjusting MV and BC at different points. I don't see how to do that in the online calc I linked above. Makes sense and I have the variable BC data for the Hornday ELD bullet but can't find a way to do that. This calculator has a single MV and BC field so I can't vary it to match the actual data. That is exactly what I am looking for in terms of 'more variables to tweak'.

I mention the enviro and MV data above. DOPE marks were -4.25MOA@300yds, -13.0MOA@575yds, -17.5MOA@675yds and -53.0MOA@1050yds.

 

[Lowlight]

That is the correct JBM if that is off you have an issue

JBM Is almost always super close, forget that trajectory chart, I want to see drop data,

I need

200 =
300 =
400 =
500 =

Etc,

The curve is meaningless I want information I can use, not a curve on a paper

 

[CoryT]

Let's put it this way, the curve should look like a curve, not a jagged line. Your plotted curve is obviously wrong. Now, WHY it's wrong is the question. If the scope is not totally calibrated to the limit of travel, you could be getting bad data in the first place, you say you needed 55 MOA, but that's reading off a dial, the actual travel in the scope may have been 44 MOA, we have no way to know. How precise and accurate are the ranges noted? Did you measure them, or are you taking someone else's word for it. I've been on ranges marked in meters but are actually yards for example. What's the terrain like over that 1050y shot. It's possible that 15mph 3 o'clock wind was a 15mph downdraft at some point you did not see.

As Lowlight says, we try to make the computer match observed reality, but it's important that we know that the observations are accurate and precise. Based on the datapoints, you can see how your data does not plot a smooth curve. That's an indication the data is bad. Note all the plots from the solvers present a smooth curve. Note how you start above the curve, get further above it, then drop sharply. Something is not right, could be the scope, the ranges, the wind, the shooter or some combination thereof plus some others.

First thing to eliminate is teh scope, if we want to use the dial as a measuring device we need to know it's delivering accurate information.

 

[1moaoff]

Give us the drop please.....

And are you sure the range are correct

 

[OGinMi]

lowlight, sorry but I can't get the drop data for the points you are asking. Local ranges only go out to 225yds. I went to that facility for only one day and got the data I mentioned in earlier posts. Can't got back there until the next regional PRS match.

CoryT, got to the local OD range yesterday and ran a scope tracking test checking vertical range up to 42MOA. I couldn't get a 60MOA target to check full range but I was hoping 42MOA should be enough to show if the tracking was linear. Given that most calculators show a 34-44MOA range for 1000yds using the 308 round, that should be enough. I checked zero, 12, 24, 36 and 42MOA points on the scope. 42MOA=43.99" at a range of 100 yards (confirmed distance with my laser rangefinder). Result with the scope elevated to 42MOA was 40.01". All the other points were within 0.25" of expected. Reset to zero and it track back to original location within 0.25". This tells me the scope tracking is fairly accurate, reset to zero is repeatable so it is not walking all over the place.

Regarding the distances of the targets at the long range, using my Vortex Ranger 1800, the distances out to 675 were within 1 yard of the range card. I couldn't confirm the accurate distance of the 1050 target but I am presuming it was within 1 or 2 yards given that the others were very close.

Given that the scope tracking results seem to show expected results (within 1% error), I don't seem to be any closer to explain that 53MOA result. Guess I am going to have to do some weird curve fit of the DOPE and interpolate sight marks from that. Won't help if there are big shifts in enviro data though.

Thanks for the help folks!

 

[CoryT]

Stop. The scope is NOT fine. You dialed 42 and got 38, that's not good. This means the numbers you are using to get the 1050 setting are wrong, perhaps by a large margin. You dialed for 675 and were a little off the predicted value, the next data point you have is 1050, where the dial is apparently useless.

You would seem to need more slope in the base, or the scope needs repair. How much down to you have from your 100 y zero? I don't see the scope make and model, how much total travel should it have?

 

[LastShot300]

So here goes the data download:
Almost any ballistics calculator tells me around 34MOA to get 1050yds at 70 degF.
Adjusting for conditions that day and sight scale factor with Applied Ballistics solver, I get a solution of at 44MOA.
The actual dial up was 53MOA! Verified with several shots.

I can assure you that given the distances involved ANY decent solver should put you almost there. Clearly a data error, operation or equipment issue. It's not the solver fault.

 

[OGinMi]

CoryT, not sure where the 38 comes from.

Here's what I got during the scope tracking test:

Zero
+12MOA up, should be 12.7" up, got 12.75" up
+24MOA up, should be 25.14" up, got 25.25" up
+36MOA up, should be 37.71" up, got 38.125" up
+42MOA up, should be 43.99" up, got 40.0" up

Any errors in the results I am presuming are my shooting and measurement skill.

I am using an Athlon Argos BTR 6-24x50 scope. It has 60MOA vertical adjustment. I have -20MOA base so I can use the most of the vertical adjustment range. There is only about 6 MOA down from zero till the scope runs out of travel.

 

[CoryT]

40" @ 100 yards is 38.2 MOA, your dial reads 42, that's not good. 40/1.047 = 38.2
36 on the other hand gave you 36.5 MOA, so you are a little over then a lot under.
You have about 50 odd minutes of travel after zero, if you used much windage to get there , you are going v to have trouble pinning the tubes.

 

[Dthomas3523]

If you got 40” with 42 moa dialed @100yds......that’s almost a 10% error.

 

[LawnMM]

What's the make and model of scope?