Advanced Marksmanship Targets USA Scope Tracking Device: Measure from muzzle or turret or halfway?

[secondofangle2]

Got the targets USA scope tracking device (http://www.targetsusa.com/scope-tools.html) last week and playing around with it.

Seems to me if you’re measuring the calibration of the *reticle* you need to measure from the target/ruler to the reticle/turret. That is the tracking error of the turret/reticle as measured on the ruler.

I’ve seen others say measure from muzzle and PRB says half way from muzzle and turrets:
http://precisionrifleblog.com/2014/0...rmance-part-1/

Now before anybody body says that’s splitting hairs - we’ll of course it is and that’s the point of checking my calibration. If you want to exclude errors greater than 5% or something big then it doesn’t matter. If you want to measure as accurately as you can any tracking error it does matter. Which is why you need a surveyors tape or a Leica DISTO laser with accuracy of inches rather than yards to measure your distance to ruler. If you don’t believe me do the calcs with 100 yards and 100 yards 2 feet and compare the results. You have just made a 0.67% measurement error - that’s the magnitude of error I’m trying to measure, and you can’t have measurement error anywhere near the quantity you’re trying to measure. It would be like trying to cut an inch off a board and having a ruler that gives you a measurement of +\- 11/16”. My PLRF15 advertises 2 meter accuracy - which could introduce >2% error and that ain’t good enough. But I digress.

My logic on the question is, why the f$&@ would barrel length matter, and if it does, why don’t any of the ballistics programs not include a dimension called “distance from turret to muzzle”?

makes no sense to me that distance from turret to muzzle would have anything to do with scope calibration. Right or wrong?

 

[secondofangle2]

Anybody?

 

[secondofangle2]

This link to the Lex Talus Corp, makers of FFS, agrees with my assessment above: http://www.lextalus.com/Articles/Scope Calibration.pdf

 

[Lowlight]

I have always measured from the Turrets ...

The error can be very small, we measured to the target in Feet vs yards or Inches and did the math, the error factor is .001+ so tiny in terms of what we can actually control and adjust for. If the scope won't adjust for it, and it's several places past the decimal point is it really that important?

But even when using a 300ft tape measure, the measurement was always from the turret.

I will refrain from commenting on the PRBlog, as they tend to make a lot of errors if you really look at what they say and do... I have had scope companies tell me, "They know just enough to be Dangerous" and that is not a good compliment if you ask me

 

[_Windrider_]

Got the targets USA scope tracking device last week and playing around with it.

Seems to me if you’re measuring the calibration of the *reticle* you need to measure from the target/ruler to the reticle/turret. That is the tracking error of the turret/reticle as measured on the ruler.

I’ve seen others say measure from muzzle and PRB says half way from muzzle and turrets:
http://precisionrifleblog.com/2014/0...rmance-part-1/

Now before anybody body says that’s splitting hairs - we’ll of course it is and that’s the point of checking my calibration. If you want to exclude errors greater than 5% or something big then it doesn’t matter. If you want to measure as accurately as you can any tracking error it does matter. Which is why you need a surveyors tape or a Leica DISTO laser with accuracy of inches rather than yards to measure your distance to ruler. If you don’t believe me do the calcs with 100 yards and 100 yards 2 feet and compare the results. You have just made a 0.67% measurement error - that’s the magnitude of error I’m trying to measure, and you can’t have measurement error anywhere near the quantity you’re trying to measure. It would be like trying to cut an inch off a board and having a ruler that gives you a measurement of +\- 11/16”. My PLRF15 advertises 2 meter accuracy - which could introduce >2% error and that ain’t good enough. But I digress.

My logic on the question is, why the f$&@ would barrel length matter, and if it does, why don’t any of the ballistics programs not include a dimension called “distance from turret to muzzle”?

makes no sense to me that distance from turret to muzzle would have anything to do with scope calibration. Right or wrong?

Forgive my ignorance, but what is this “device” you speak of? And always to the turrets is how I’ve done it.

 

[Lowlight]

The Scope testing device they made for us in Alaska

 

[earthquake]

I always measure to the turrets too. May as well, right? Makes the most sense. However, I'm not sure you could split the difference between the turret and halfway point to muzzle vs. some slight curvature/bending in your tape between Target and scope, flexing/stretching of the material when trailing it out, or thermal expansion & contraction of the tape itself. Ever measure that? I haven't, but may do it just to see.

 

[secondofangle2]

The deal is, every time I think I have an accurate measurement, I re-measure again at a different location and get a different result. My own error rate for measuring the scope error rate is on the order of 0.5% to 1.0%. I would like to measure the correct calibration with much less error than that, so that I don't build a scope tracking error into my ballistics solution that really is a scope tracking measurement (ME!) error!

I have discerned the following variables which introduce error into the procedure:

1.) System movement during testing. The device pictured above PARTLY but not completely eliminates that. The device weighs 30# but can still move, especially if you don't tighten the stop nuts on the legs. I bought a 26.2# lead brick to add weight to it. Alternative, if you're on a fixed bench, is to put a board over the fore end of the "T" and use clamps to clamp it to the bench. Also, the rubber feet help with slip but are partly compressible, so if you hold down the device with your hand when you turn the turrets, you move the system.

2.) Measurement error from turrets to target. I have mostly eliminated that with a 300' tape, but the Leica DISTO D2 (resolution, 1/16th of an inch) arrives today to eliminate ANY error there. Each foot at 100 yards introduces 0.33% error as I stated above, and as is corroborated in the link to the FFS page on the topic.

3.) Leveling of components of the system, scope and ruler. I have eliminated most all of that by using a fixed level on the board the ruler is affixed to and using a simultaneous plumb bob hung from the board.

4.) Parallax. I think this is a huge one. My TT and my NF ATACR still have some parallax that I can't adjust out of them at 100 yards.

5.) Ability to resolve marks on ruler at 100 yards that are smaller than 1"

I know this may sound like overkill but I'm a medical researcher with statistical training, and I know that measurement error is a big deal and repeatability is very important. If I cannot repeat the measurement, why am I even building it into my calculations? I would like to be within 0.5% or less error. If I know my error rate, that is, between different measurements, I have a measurement error of 0.5%, then I know to dismiss differences smaller than that. So, if I get that my scope has 0.3% error, I say, well that's within my margin of error of my measurements, and I'm not going to make any adjustment to my click value in TRASOL.

I will report back my results. But I'm willing to bet, that if you use a 96" ruler/target and run your scope 25 MRAD or 90 MOA on multiple different occasions/locations/setups, you will find what I have found - measurement variability that is very close to the error you are trying to measure in the high end scopes.

 

[_Windrider_]

The Scope testing device they made for us in Alaska

Ah. Got it. Saw that in your pics.

 

[tnichols]

In another photo of this device, I noticed the main “body” was long enough to accept gym weights as ballast. Is this version heavy enough without ballast to keep it from moving around as you manipulate the turrets?

 

[Lowlight]

Yes,

They use solid steel framing the original one with the weight mount was hollow. That was the Gen 1 version it has since changed, twice.

It weighs like 30LBS as pictured above... if your scope is moving dialing it, your scope sucks

 

[tnichols]

Yes,

They use solid steel framing the original one with the weight mount was hollow. That was the Gen 1 version it has since changed, twice.

It weighs like 30LBS as pictured above... if your scope is moving dialing it, your scope sucks

Thank you for the information.

 

[Lowlight]

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[secondofangle2]

Agree with video that you must lock leg screws with nuts to prevent movement.

The leg screws can be a pain to set up. When you tighten them the system moves. If you are trying to have your scope at top of ruler on zero, hard to do. I suggest instead getting it close then use the elevation knob to adjust to the top of the ruler. Just record the offsets.

I spend a lot more time leveling than he, if he did it at all.

I got my 26.2# lead brick yesterday. It really really helps with stability. A bag or two of lead shot would likewise work wonders.

I do NOT recommend making marks on the board. Too much room for error. Screw actual rulers to the board and make large marks on the board every 6-12” for easy Visual ID

I think you optimally want the scope to travel 25 MRAD or 100 MOA to find small errors.

I used the Leica DISTO D2 last night and it was teats.

It it was the first time I got repeatable results over and over. Some of the same corrections from previous measurements but some past measurements were way off. I suspect system movement, and inaccurate distance to ruler for those errors. And maybe parallax too.

 

[secondofangle2]

http://u.cubeupload.com/Secondofangl...A47869BCD.jpeg
http://u.cubeupload.com/Secondofangl...B48349E86.jpeg
http://u.cubeupload.com/Secondofangl...C42C5AA36.jpeg

 

[secondofangle]