Range Report Question for you experienced LR shooters

jrob300

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I've read a little on this subject. Now I want to know how you guys make adjustments when ballistic data does not fit your field data.

I'm shooting 208 Amax's at 2860 fps, 4000' ASL.

JBM gives 1.0, 3.2, 8.3 and 10.9 mil for 300, 600, 1100 and 1300 respectively.

Field data shows 1.1, 3.1, 7.8 and 9.6.

No matter how I manipulate the variables in JBM, I have not been able to duplicate my field data.

So, do you get it close and bias toward long range accuracy and then confirm with field data?

I'd like to get out to 1 mile soon, and I'm sure the data will get me close, but misses are getting really hard to spot and I don't want to spend all day dancing around the steel.

What do you guys do? Comments, questions, advice, or helpful hints from those wiser and more experienced than I would be greatly appreciated.

Thanks,

John
 

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Re: Question for you experienced LR shooters

Is your hundred yard zero exact? Does your scope track exactly? Does the Hornady AMax match the G7 curve exactly? Is your chrono data exact? Any of those including head and tail winds will throw you off. JMHO
 

ChadTRG42

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Re: Question for you experienced LR shooters

That's a big difference between your field data and computed data. Have you tracked you scope to make sure you are getting .1 mil adjustments? Is this a confirmed velocity on the bullet? Is this a 100 yard zero? Is this yards or meters?

Somethings not adding up right. Here's what I'm showing with your 208 with a G7 BC of .323 at 2860 at 4K feet, with standard conditions. If it's hot where you are, bullets have less drop then when it's cold, so that can make a difference. But it's pretty far off still.

Range Elev
(yards) (mil)
0 ---
100 0
200 -0.42
300 -1.05
400 -1.77
500 -2.58
600 -3.46
700 -4.41
800 -5.46
900 -6.6
1000 -7.84
1100 -9.21
1200 -10.71
1300 -12.37
 

AQC440

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Re: Question for you experienced LR shooters

Are you shooting across "dead flat ground"?
Winds hitting the face of a slope somewhere down range could be causing updrafts effecting POI. I know you are familiar with bullets impacting high / low when shooting on slopes.
And finally, boiling mirage coming up from the ground can cause your aiming point to appear higher then it actually is...
 

jrob300

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Re: Question for you experienced LR shooters

Thanks for the input.

FNP and Chad,

Yes, 100 yd. zero and it's as close to zero as I can get with .1 mil adjustments. About 1/8" low/1/8" right at 100 yds.

I have *not* verified exactly .1 mil/.1 mil for my adjustments. It's a Falcon 4.5-14x44. This would be worth checking, as there are times when I could swear I'm getting a lot more than .1 or .2 mil at the target. I usually chalk it up to my shooting.
wink.gif
I'll be getting a 6-24 Viper PST soon, so I'm not sure how much work I'll put into this.

I don't know how to confirm my velocity other than to borrow another chrono. These velocities have been pretty consistent with this load across a variety of temp. (H1000) over fall/winter/spring in Montana (0*F-75*f so far).

I'm using G1 for my JBM. Should I be using G7? Looks like it's even further off.

I was shooting into a 5-8 mph 12 o'clock headwind (.1 mil left wind correction)which makes the field data even wierder to me.

It's entirely conceivable that my velocities are falsely high and my adjustments are generous. I've been extremely amazed at the performance I've been getting out of a 22" barrel.

AQC,

No real mirage to speak of this particular outing and the place I shoot, I fire fom a small "mound", probably 20-25 feet high and then it's old lake bed. Dead flat.

Keep the thoughts coming. I'm very appreciative and continually amazed at the wealth of knowledge on this site.

John
 

ida83704

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Re: Question for you experienced LR shooters

You shooting flatter than your JBM data.

Since you put 4000' ASL, I'd look at your barometer settings. maybe switch to uncorrected pressure and 0 elevation.
 

ida83704

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Re: Question for you experienced LR shooters

I can't make your actuals work either.

What did you use to determine the distance to targets?

using these inputs
.648 G1 BC
2860fps
26.00Hg.
75F

I get
7.8 mills at 1050 yards
and
9.7 mills at 1200 yards

your 300 and 600 yard dope looks reasonable.
 

jrob300

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">I can't make your actuals work either.

What did you use to determine the distance to targets?

using these inputs
.648 G1 BC
2860fps
26.00Hg.
75F

I get
7.8 mills at 1050 yards
and
9.7 mills at 1200 yards

your 300 and 600 yard dope looks reasonable. </div></div>

I ran 68*f and 50% humidity.

Distances were acquired by leapfrog LRF'ing, so there could be *some* error there (for instance, if we were not exactly line of sight), but I didn't think it would be this big. I do know that as things get more parabolic (longer distances)that small errors become much larger misses.

We might be off by 10 or 20 yds., but I'd be shocked of it was 100. Would a GPS be more accurate than the LRF technique I described (my Nikon 800 is supposed to be good to +/- 1 yard, x3 for each leg of the leapfrog (500 yds. at a time)= +/- 3 yards, right?)

ETA: it might be time to buy the freaking Leica!

John
 

bohem

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Re: Question for you experienced LR shooters

Have you double checked your scope height above bore line measurement to know you're spot on there? Even being off a tenth of an inch will throw the calculator off more and more as you get further out.
 

Rob01

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Re: Question for you experienced LR shooters

Scope height above bore comes into being more critical the closer you get as in from 50 yards and in. Out at 1300 yards there is only a .2 mil difference between 1.5" height and 2" height. No difference at 1000.
 

bohem

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">Scope height above bore comes into being more critical the closer you get as in from 50 yards and in. Out at 1300 yards there is only a .2 mil difference between 1.5" height and 2" height. No difference at 1000. </div></div>


I must have it backwards in my head, I'll check that again.
 

jrob300

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Re: Question for you experienced LR shooters

You guys have been very helpful.

The two variables that seem to have the greatest effect and the biggest question mark over them are:

<span style="font-weight: bold">Actual elevation adjustment vs. marked elevation adjustment

Measured distance vs. actual distance
</span>
Since others of you have had pretty good luck with JBM, I'm going to assume that some combination of error in the above two variables is my problem.

I'll be getting a new scope soon, and will verify the elevation adjustments. That will take care of that variable. I'm guessing this is the lion's share of my error.

I have no LRF that can shoot this distance in 1 reading. We leapfrogged it, and may not have shot a straight line + the compound error of 3 LRF readings.

Would a GPS be more accurate? How do you guys verify your distance on ranges over 1200 yds?

ETA: <span style="font-weight: bold">Actual muzzle velocity</span> could be in question also. I'll see if I can borrow someone else's chrono and verify my numbers.

John
 

Short-bus

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Re: Question for you experienced LR shooters

I ran some trajectory correction on your numbers, and it looks like (considering what little details I have on everything) that your velocity is higher than you're stating. Just note that i'm basing that off very little input data to confirm, and isolate the real cause of the discrepancies.

I shoot over a chrono quite often, usually only when doing some load development as it get's me pretty close, and at least let's me know if i'm going in the direction that I intend.

I confirm a load by shooting at 700 yards at a steel target, and take the real world drop data, and all the atmospheric data at the time and backtrack to find the real velocity. After that's done, I move back, or closer, whichever I choose, and shoot another range and see if the data is good. That usually works out well for me. 208 amax's seem to be in a world of their own, and i've found more than once that the calculators don't always predict accurately what the amax's will do.

Branden
 

ida83704

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Re: Question for you experienced LR shooters

Your GPS should indicate your elevation.

GPS range measurements can be more accurate. It depends.

One way to check is take GPS measurements when you are taking LRF readings. If they are comparable then your end to end should be GTG.

2860fps from a 22 inch barrel seems pretty fast.

JBM tracks well for me when I put in the correct data.

Always believe the bullet, can't remember who said that first.
 

TCA4570

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Re: Question for you experienced LR shooters

Do you have good dope at 600 and 1000?
Having 100 yard zero is just a little better than chrony at how far?
By getting dope at these two ranges, you might be able to figure out better info.
just my .02
 

jrob300

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Re: Question for you experienced LR shooters

Good thoughts.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">2860fps from a 22 inch barrel seems pretty fast.
</div></div>

Yeah, I thought so too, as my OEM barrel which was 24" didn't get much faster (2900 IIRC).

But my shooting partner rebarreled at the same time I did and he's getting 2960 (perhaps a tad fast, but not unreasonable) from the same load from his 25", so I'd think if my chrono was optimistic, we'd see higher numbers for his too.

I'd be more concerned about this if my elevations were *more* than JBM predicted, but like DustRemover pointed out, if anything I'm <span style="font-style: italic">faster</span>, which *really* seems odd.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">
Always believe the bullet, can't remember who said that first. </div></div>

This is ultimately ALL that matters, and I know that. Anomalies bug me though. If I collect enough field data, nothing else really matters. But since JBM works fairly well for everyone else, I'd like to know WHY it's not for me.

The speed of the bullet and the accuracy of adjustments are what they are. The one thing that could REALLY screw me up here is my method of determining distance. If that's innaccurate, it will raise it's ugly head in the future.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">
One way to check is take GPS measurements when you are taking LRF readings. If they are comparable then your end to end should be GTG.
</div></div>

I will try this our next outing. Should be soon weather permitting.

Thanks again,
John
 

jrob300

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TCA4570</div><div class="ubbcode-body">Do you have good dope at 600 and 1000?
Having 100 yard zero is just a little better than chrony at how far?
By getting dope at these two ranges, you might be able to figure out better info.
just my .02 </div></div>

Yeah, I have field data for 300, 600, 1100 and now after Tues., 1300. The thing that seems really odd to me is I have *more* elevation correction than JBM suggests at 300, then less at 600, 1100 and 1300. The 600 is close enough to be within normal error, but the 1100, and 1300 are WAY off. (see first post for actuals.)

John
 

Lindy

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Re: Question for you experienced LR shooters

Through all of this you have mentioned that you were shooting at 4000 feet ASL.

If you want a ballistics program to provide guidance for you, it's necessary to not use the altitude, but to give the ballistics program the actual station atmospheric pressure. See:

Barometric Pressure and Ballistic Software

There are a number of other factors which individually or in combination can lead to differences between what the program calculates and what you observed in the field. As many of those need to be checked and eliminated as possible.

Sources of Ballistic Program Inaccuracies

When in doubt, believe the bullet.
 

jrob300

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Through all of this you have mentioned that you were shooting at 4000 feet ASL.

If you want a ballistics program to provide guidance for you, it's necessary to not use the altitude, but to give the ballistics program the actual station atmospheric pressure.
</div></div>

Lindy,

That's a really good point that I had not considered. When put like that elev. becomes a very rough means of calculating one factor of resistance, how "thick" the air is. Barometric pressure would be a direct measurement rather than a derivation. Correct? IIRC, barometric pressure is what's used by altimeters to derive altitude.

I continue to learn.

I'll read your two links.

Thanks,

John
 

ida83704

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Re: Question for you experienced LR shooters

Any update on this?

I've run several scenerios and they all point to range finding or some freek bullet issue.
 

marduk185

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Re: Question for you experienced LR shooters

for what its worth ive experienced very similar dissatisfaction with jbm not matching my actuals. i get much flatter actuals than jbm when it comes to my moa adjust for various distances however, for me, i noticed this last outing that the mil column lines up accurately if i use mildot holdovers but if i dial in the moa listed in jbm im way off. im beginning to think my moa turrets arent tracking accurately. they seem to run up and back to zero repeatably but perhaps theyre not really giving quarter minute clicks. any way just a thought.
 

jrob300

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">Any update on this?

I've run several scenerios and they all point to range finding or some freek bullet issue.

</div></div>

No update yet. Perhaps early next week.

It's been raining cats & dogs here and supposed to continue through the weekend. We probably wouldn't even be able to see the gong even if we could navigate all the mud.
grin.gif


Lindy's links showed me I'm feeding the wrong info to JBM for Altitude/Barometric pressure. I need to find a way of measuring station pressure.

I'm putting my money on LRF measurement error/user error and not quite .1 mil actual adjustments, although I've talked to more than a few guys that have said they got similar results w/JBM. Perhaps we're just making the same mistakes...

We'll take GPS readings next time out to double check our distance and the scope is getting replaced as soon as the Viper PST's are out, so that part is moot.

John
 

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Re: Question for you experienced LR shooters

You may want to track test the new scope - I used a large piece of cardboard and drew out precisely a verticle (plumb) line with exact moa graduations, up to about 50 moa. At 100 yards with the rifle steady you can see quickly if the clicks are correct and consistent over the travel range...might give you confidence in the scope although your issue seems likely something else.
 

jrob300

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Re: Question for you experienced LR shooters

This is very good advice. The scope I have now, a Falcon Menace, has a big question mark over the accuracy of it's adjustments, but it is what it is. Perhaps it's just a pipe dream, but I'm really hoping the Viper PST is a class act. Especially since I just read a post where a guy has a scope that the adjustments change as mil's go up. That would be hard to deal with.

Still been raining here. This is our wettest spring in years.

Praying for a nice sunny day.

John
 

ida83704

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Re: Question for you experienced LR shooters

Did you ever figgure out what the issue was on this?

I did a test at 1214 yards, using GPS, with JBM and was within 1.5moa(20-ish inches)
 

jrob300

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Re: Question for you experienced LR shooters

Sorry, no good update on this. I still haven't been able to get back to my LR spot due to mud, but I used the data I culled there this weekend for a shoot and had hits at 1535, 1575 and 1900, so I'm not far off.

It taught me that even though your scope may not be accurate, field data will get you there.

I'm still guessing the scope is generous. It's a moot point now, as the scope puked it's guts this weekend. Parallax adj. is toast. A new one is on its way and it'll probably be different.
wink.gif


The PST's will probably come in just in time to start all over again.
grin.gif


John
 

jrob300

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ida83704</div><div class="ubbcode-body">Did you ever figgure out what the issue was on this?</div></div>

Well, I think this is resolved. We took a GPS out and checked distances. It won't read over 999 in yds, after that it switches to miles. So we used a combo of GPS and rangefinder and found that our 1100 was 1070 and 0ur 1300 was 1260. The Falcon is now long gone, it died. RIP. But I'm assuming that the mils were off, too.

We set up new targets at 500, 1000, and 1500 and got new data on the Vortex Razor. Yes, I validated it ahead of time. The mils are a little fat, not perfect, but workable. All three distances worked out to within .1 mils of JBM data. Cold bore hit center mass at 1500! YAY! Mystery solved. Or, at least no longer relevant. Thanks for everyones input.

John
 

ida83704

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Re: Question for you experienced LR shooters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body">
We set up new targets at 500, 1000, and 1500 and got new data on the Vortex Razor.....
All three distances worked out to within .1 mils of JBM data. Cold bore hit center mass at 1500! </div></div>

That's pretty cool