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Gluv

Scope Calibration

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13 hours ago, ds1 said:

VarmLR, with reference to that article. It is now several years old and some of the scopes have evolved. With reference to the March scope on that test I remember asking March Optics- they told me that the scope sent for that test was a test model and for whatever reason I forget had a different system of milradian in it  - there being 6000or 6300 or 6400 degrees in a circle, depends which criteria you use, as a miltadian is an angular not linear measurement.

 

Yes, mils are approximated depending on manufacturer. In theory however, there is no equivocation on the derived units for a Milliradian, just on how some approximate them.

One milliradian is derived from a unit circle with a radius of one unit, using an arc divided further into 1000 milliradians per radian (ie the angle subtended by an arc of one radian divided by 1000) equating to 2000Pi per circle.  2000 Pi approximates to 6283.185.  For the most part, the military (the UK army for one) use 6400 which is used on every military compass that I have used, which is no surprise since 6400 is the NATO standard for a Milliradian.  It is quite important that the military standardise the unit because artillery sights used to depend on very accurate bearings!  

6300 units AFAIK is a Swedish derived unit, used to simplify divisions but I'm unsure if any of the scopes listed would use that unit.

One issue that the scope test, interestingly, did not cover is that all approximations, including the use of 1cm/100m contain an angular error, which is compounded as the angle increases.  It is a very small error and largely inconsequntial though for target shooting.  For example, using 1cm @ 100m there is an error of 3.3 x 10-7 which is compounded to 0.03% assuming 30 Mils is 30cm@1000m. Therefore, one can probably say that no scope will ever track exactly for that reason.

The value of a fine hash true mil-ret in the FFP, or an MOA ret come to that with MOA turrets, takes away uncertainty caused by error at any distance.  The value of mils or moa in a FFP  remains for getting shots onto target at any range as long as you know where the fall of shot is and can spot it.  It makes it easy then to dial in corrections to get on target rapidly, even if the dials do not exactly correspond (that's what the correction factor's for after all).

 

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Please explain to me why 1 cm at 100M is an approximation, by my understanding this is exactly correct and uses no approximation and has no error but I am willing to learn.

We also tested one of the original March scope and it was running at 6400, they are also now (in my experience) and offer true miliradians without approximation.

6400 as a value is used in the military as a nav method etc but this is not what is in S&B etc scopes.

 

regards

 

Ewen

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1 hour ago, Deserttech Europe said:

Please explain to me why 1 cm at 100M is an approximation, by my understanding this is exactly correct and uses no approximation and has no error but I am willing to learn.

We also tested one of the original March scope and it was running at 6400, they are also now (in my experience) and offer true miliradians without approximation.

6400 as a value is used in the military as a nav method etc but this is not what is in S&B etc scopes.

 

regards

 

Ewen

The approximation error admittedly is very small.  The error has a mathematical explanation which you can read from the WolframAlpha resource here:

http://www.wolframalpha.com/input/?i=(abs((((arctan(0.1%2F1000))*1000)-0.1)%2F((arctan(0.1%2F1000))*1000)))*100

The error is only very tiny and is there because, whilst one cm is given as the length of the arc subtended by 0.1 millirad at 100m, it is based upon the Sine of the angle being very closely the same as the value used of that angle itself, hence the subtension being approximately equal

{\displaystyle {\text{subtension}}\simeq {\text{arc length}}}.....ie "approximates to"

 "Theta" is the exact angular distance denoted by:

Theta (trig)= Arctan(subtention/range).  This is the exact or actual length of the arc.

We though use the close approximation which is slightly different being:

Theta (radians) = subtention/range which is a good and close approximation, hence 1cm/100m

The maths tbh is not something shooters normally go into as we simply use the approximation as the exact value, as you have observed.

Here's a good graphical explanation cut and pasted from Wiki which summarises it and explains it more clearly and readily than I have tried to do!

330px-Observed_angle,_arc_length_and_sub

For small observed angles like the Milliradian, the length of arc subtended by the small angle (theta 1 in green) approximates closely to the vertical subtension (yellow), the smaller the angle, the closer the approximation, hence the less the approximation error.

 

 

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Hol

On 24/01/2018 at 8:47 AM, VarmLR said:

 

One issue that the scope test, interestingly, did not cover is that all approximations, including the use of 1cm/100m contain an angular error, which is compounded as the angle increases.  It is a very small error and largely inconsequntial though for target shooting.  For example, using 1cm @ 100m there is an error of 3.3 x 10-7 which is compounded to 0.03% assuming 30 Mils is 30cm@1000m. Therefore, one can probably say that no scope will ever track exactly for that reason.

 

Holy crap. You're surprised an error that miniscule in a small arms optic wasn't covered?!  I've not checked your maths, or whether the chord/arc  'error' you've stated was cm or m , but you've stated  an error value of 0.00000033, lets assume the measurement was metres, that's an error of 0.0003mm ..at 100metres. so about 200 times finer than a human hair  -  Weird they didn't mention it ! :lol:  :) 

Haven't followed your subsequent calc, but you still appear to be talking in 'hundredths of a millimeter' for a large change at 1000m.  Values in both cases that wouldn't be even remotely empirically observable.

I think it's safe to say that at small arms ranges and elevations, arc/chord subtension issues are  so close to zero as to be completely ignorable.

 

As regards the various other posts / posters discussing repeatability and calibration stuff;  I never understand why anyone would choose to perform an optical calibration test by shooting. One is then testing the shooting system as a whole; not the optics alone.

I'd recommend this ...as always, I'm horses, not zebras, so:  KISS (Keep It Simple Stupid):

Clamp the rifle (eg black and decker workmate) and simply observe a ruler placed vertically at exactly 10m, or a tape measure at 100m.

Then dial on, say, 50 clicks, and see where the ret has moved. (Calibration) Then dial it back. Does it go back to the start point? (Repeatability).

Do it a bunch of times for different bunches of clicks. If the calibration error is hard to see visually, throw it into stark relief by winding on big corrections and returns.

Job done.

Simples.   :)

 

 

 

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Matt,

.          You could indeed do a vertical calibration of the scope optically as described.

But would this indicate whether any cant was present-cant of course displacing shots  to the side of the vertical plumbed measure line used to calibrate the scope clicks.

Shooting does that too,though of course adds shooting system variance,if any,to the whole process.At the BR level,that won't be much,with sub .25 moa groups for 5 shots.

   Cant effect  isn't negligible-ball park at 1000y,say 300"  adjustment to be zeroed,then each  1 degree of cant will displace the poi  some 5 inches horizontally to poa.

At 600y,with 5 degrees of cant, needing 13 moa elevation,you'd hit  nearly 9 inches to the side (and  nearly half an inch low). 

(Rule of thumb calculation for horizontal displacement : elevation needed to hit target at the distance,plus 3moa (or 1 mil) multiplied by the sine of the cant angle. So that's (13+3xsin5) which is 1.4moa or 8.8 inches .Vertical is (13+3xcos5) which is 15.94 moa,ie .06 moa low (.4inches).

 

So If your scope is 'canted' out of true vertical,you'd  want to know and correct it.

Holes on paper may also have some psychological clout/reassurance;and we're supposed to enjoy shooting. If we can't  :-)   do it  adequately,perhaps better we  know,with improvement an option,rather than blaming the gear.

gbal

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1 hour ago, brown dog said:

Hol

Holy crap. You're surprised an error that miniscule in a small arms optic wasn't covered?!  I've not checked your maths, or whether the chord/arc  'error' you've stated was cm or m , but you've stated  an error value of 0.00000033, lets assume the measurement was metres, that's an error of 0.0003mm ..at 100metres. so about 200 times finer than a human hair  -  Weird they didn't mention it ! :lol:  :) 

Haven't followed your subsequent calc, but you still appear to be talking in 'hundredths of a millimeter' for a large change at 1000m.  Values in both cases that wouldn't be even remotely empirically observable.

I think it's safe to say that at small arms ranges and elevations, arc/chord subtension issues are  so close to zero as to be completely ignorable.

 

As regards the various other posts / posters discussing repeatability and calibration stuff;  I never understand why anyone would choose to perform an optical calibration test by shooting. One is then testing the shooting system as a whole; not the optics alone.

I'd recommend this ...as always, I'm horses, not zebras, so:  KISS (Keep It Simple Stupid):

Clamp the rifle (eg black and decker workmate) and simply observe a ruler placed vertically at exactly 10m, or a tape measure at 100m.

Then dial on, say, 50 clicks, and see where the ret has moved. (Calibration) Then dial it back. Does it go back to the start point? (Repeatability).

Do it a bunch of times for different bunches of clicks. If the calibration error is hard to see visually, throw it into stark relief by winding on big corrections and returns.

Job done.

Simples.   :)

 

 

 

I don't disagree.  The point, it seems, was missed. It was out of interest and not out of any practical application or consideration.  Perhaps it's better if I don't  bother contributing...perfectly happy just to learn off others as there remains a wealth of know how here.

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George, you'd be muddling dependent variables if you were to try to assess cant at the same time as check scope calibration and repeatability.

In sequence and separately, one at a time, or the output is meaningless.

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Mark, the classic male relationship weakness ....."Cant explain"

Matt,yes despite complex ANOVA designs I broadly prefer the one variable change at a time,where possible/convenient. BUt I note from the video posted earlier in the thread,Bryan Litz sems to think shots on target can help both.

  It may be that the use of 'cant'to incluse/be a non vertical orentation of the scope crosshair is a tad misleading (as UK use can include shooter induced  'tilt/cant' of the rifle (and therfore vertical in scope) away from strict horizontal/neutral.Indeed some targeteers  deliberately add cant to counteract ...well,quantifiable aspects of the devils work using other variables,whether spin/shooter position etc etc.

    Whatever,the main point was that 'optical' might well give answers to calibration (does  xmoa (ormil) dialed in by clicking actually give the desired ccorrection on target,and does it do so reliably every time and return to zero when freversed),but can a non firing method check for cant (bullets impact to the side,without any horizontal clicking). If not,then somefiring will be needed-ssparately perhaps,but I'm not sure I see how any other variables will be removed from 'cant' firing,that were there in the 'vertical tracking'test?

     Seem to me always best to check-at least- by actual firing,for almost any sighting/load issue and applied 'solution'....holes in the paper afre the proof of the cooking,as it were.  Otherwise,we could all get someone (I'd favour Mr Litz) to do the math(s),and just not shoot at all,confident that perfect centered hits were assured,so did not actually need to be fired. If only......we could still have  math(s) as a hobby,given a reliable and caliibrated  ballistics wizzard  to do them....hmmmm....

"In theory,theory and practice are the  same,but in practice they may not be"...Yogi Bear(a)...time to rechamber in  30  Boo Boo,lest the uncontrolled Valkyries attack.

The optical approach has merit of course,with a suitably fine measuring rule,and is relatively weather immune,and much reduces the noise of human error.And of course as ever,consider wrt target size-just count the hits/misses (though a proper WEZ analysis will be more revealing,and cost a lot less in ammo)-though isn't a hundred plus shots what the well read,cellared and armed hobbyist should welcome?   :-)

My trust in maths (plural,just in case all math are not equal) is great,but as said,something  reassuring about holes in the predicted and desired places (noise is inaudible!) atb,on all these gentleman's essentials!

g

 

 

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I think Yogi Beara's thing doesn't apply to empirically calibrating an optical instrument: Calibration is the act of empirically assessing the theoretical click value. It would apply were one to decide that calibration is for cissies and to trust the manufacturer's claimed click values and, yes,  it would apply to the subsequent use of said calibrated instrument in a 'system': Calibrated scope doesn't guarantee uncanted fire, but it does mean that where a cant effect is seen, the mechanics of the scope itself have been ruled out.

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  Matt -Can optical calibration as you described it actually identify cant? It seems able to calibrate the actual scope click values at least as well as can be discriminated by eye by comparing  the horizontal cross hair to the ruler markings used on the vertical. (Are the claimed -what you  describe as 'theoretical-' 1/4 moa click(s) actually moving  1/4 moa ( or just something close to  1/4 moa;and is any discrepancy  consistent over the adjustment range (or does it get less close to 1/4 moa at extremes?) 

      I think "cant'  determination perhaps gets to a higher order checking of the scope.Most shooters don't need/want cant -the situation that obtains when the scope's vertical is not straight up/down,but which will induce some unintentional horizontal. (The formula for estimating has already been given)  

Best for Long Range shooting is a perfectly level rifle,so that the vertical and horizontal ascope adjustments are independent.Cant is  eliminated via a simple sight level-the familiar bubble indicator,fixed to scope (etc) where  the shooter can easlity check visually.Instalation is done by holding the scope's vertical crosshair fixed in relation to  a reference plumb line,and the bubble level is fitted to read level.

   The tall targer test-as per the litz video- can confirm/not that the scope is tracking true vertical (as well as checking calibration,of course-the main objective). But this will only work IF the the crosshairs actually  move straight up/down. BUT if the vertical crosshair in the scopee is installed at manufacture at a slight angle to the mechanism that moves the crosshairs (the clicker) there ill be a tracking problem.Such ar not very common,but even the best make scopes sometimes perform modestly on test (the PR blog had poor results from  a March,and  a new spec S&B las year).The tall target test can reveal any such issues,so it's worth doing-by firing a tall target test to calibrate,and simultaneously check for cant. Effects of course increase with real shooting range (100y "should"not be an issue-but rabbits have been shot over/under by 2 inches at 500y,despite meticulous shooting solution inputs-but no calibration correction.

   (Intentional cant,which some shooters use,is fine,so long as the sights are level,and 'forced' cant-from an awkward position eg,can be allowed for via the 'cant rule of thumb' formula.

Bottom take away line-best to never take anything for granted,whatever it 'says on the tin',if it can be measured with confidence and accuracy-and actually,fairly easily here,if you get a wind free  half hour.

gbal

.   

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George, you are conflating click calibration (ie how the scope mechanicals perform) and cant.  I'm genuinely at a loss to understand why you keep bringing cant into a calibration discussion. Separate and sequential. :)

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I see the difference.My point  is that the advantage of doing a TallTarget Test with live firing to check calibration is that this will ,at the same time-which isn't  the same as 'conflating' the concepts-check for any cant induced by internal misalignment of the scope crosshairs with the click mechanism.

 SO live firing test for optical calibration is one method-but so is justan optical alignment check without live firiing.BUt only the first method can also check for internal cant induced horizontal error.

  SO the tall target test firing has two outcomes,and is worth doing,especially in the absence of an alternative check for the second possible ''can't  error. "Two birdswith one stone' sort of,or at least with two or three groups of 5 shotswith vertical clicks aaround 10 moa bewteen them.

 Optical alone will check calibration-but not the second issue.Holes on paper in the rightbplaces is probably good for confidence too,but not essential.The downside to not shooting a TT test ,is unresolved doubt  about the possible,though not common,horizontal error.Of course,if you don't know about it,no worries-unless you  get such a scope.

"Don't take it for granted that the crosshairs move actually as advertised.Don't take it for granted that the crosshairs are actually level,and track exactly vertical" (Litz,as in his Tall Target Test video-I'm happy to be conflated with him on this point.)    :-)

 I suspect some/many  don't even do the tall target test to check click calibration,and are then puzzled by elevation errors, and attribute it to error in  their ballistic solver.

Shame,there is an easy check.

'Separate and sequential'-OK,but the live fire Tall Target test is 'synoptic"....ie it  provides data on both;so why not do it.

     Seems sensible,as there does not seem a convenient 'separate but sequential'  vertical tracking test'   I suppose you could do the tall target without firing (calibration) and  the  tall target with firing (vertical alignment)....OK,you'd also have some correlational/comparative data on the two assessments of calibration.

But  don't do them on the same page...LItz writes "The tall target test outlined previously for calibrating adjustments can also be used to confirm that the scope is tracking  straight up....the tall target test (may ) reveal a tracking error",but I admit,with a carefully placed photo,it's printed on the last few part lines on one page,and the top couple of lines on the next. 

 As Litz conflates it "the good news is that the problem of uncertain sight adjustments  can be fixed with one trip to the range.Here's how to do it...' (The tall target live firing test).

Let's leave it at that,since the actual proceedure is very clear,and should answer both uncertainties ...err...simultaneously.

g

   

 

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10 minutes ago, gbal said:

I see the difference.My point  is that the advantage of doing a TallTarget Test with live firing to check calibration is that this will ,at the same time-which isn't  the same as 'conflating' the concepts-check for any cant induced by internal misalignment of the scope crosshairs with the click mechanism.

Well, no. :)

It's back to muddling dependant variables.  If you go straight to a tall target shooting test, and get 'lateral'; you will have nil idea as to the cause: cog jump or ret misalignment or scope not level or rifle not level or a bit of each or a bit of some.

 

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If you want to check the tracking of a scope you need to test JUST the scope.

If you put it on a rifle and test shot then you are testing the scope, the rifle, the load and the bullet head.

Surly if you want to test the tracking of the scope you mount JUST the scope on something that does not move, make sure it is level and the track it.

Anything with more than one variable is open to question.

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OK,Matt-won't the zero ing check (the first live fire group,)show whether all these shooter error variables  are actually occuring ....IF the scope's vertical  is out,the lateral will only gradually emerge as  more vertical is dialled in-hard to see why the horizontal would be incremental/ accumulate if it's the same raft of shooter errors.**

    Alternately,how do you -separately from the TT test-check for lateral using a different method,immune from this raft of shooter error,some of which may  be present as likely for the vertical  test,when done?

** ie     IF the horizontal gradually emerges as vertical clicks are dialled in, does it not begin to look like a consistent incremental internal scope fault in vertical tracking?

I was going to check all my aperture sights,but I've lost the will . And since the aperture's adjustment mechanisms are actually exposed,it's not neccessary to actually shoot the rifle-so where is the fun in that?    :-)

g

PS Avian,without firing,how do you check for the second possible manufacture error-the scope does not track true vertical(so shots are increasingly dislaced sideways;this is indendent of whether the calibration is accurate (one click really is 1/4 moa,as marked)

   As suggested ,a pure optical test may be fine for checking click values-though Litz et al just shoot carefully-as it does both tests at the same time. Ditto the 'box test etc...clickmout and reverse.....first and last shots should touch (perfection would be same hole).

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To check accurate vertical tracking get a tall target printed accurately with increment of known value, say 1cm.

Place it at exactly 100m, measure with steel tape not range finder, and set the scope up on one point.

Then dial scope and see if it moves to the correct position on the target.

As with any experiment if you change more than on variable you are looking at more than one thing.

If you use bullet placement you are looking at:

Scope alignment on rifle

Cant of scope on rifle

Rife itself

Shoot error

load variation

neck tension

bullet variance

etc

You can do the same with left and right.  Also for vertical tracking if you ensure that the line of the target is exactly vertical you can check that as well

To test the scope, juts test the scope

 

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I’ll throw my 5 pence in As this ems to be picking the fly shite out of the pepper

What I Have ‘done’ to check scope ‘installationis use a tallish inverted T target at a short range.

the T is drawn on the already in place target with a spirit level for both the bottom horizontal and vertical line.

Check the rifle’s zeroed on a dot on the target, then by only aiming at the junction of the T and adding good hands full  of elevation shoot rounds up and down the vertical, coming back to the zero of the junction. You then see if the vertical groups matched the settings and the groups tracked up and down the line. This gives you your  actual click value and also if the scope’s on the rifle ‘vertical’.

As this is actual results with the scope and rifle combination ‘as is’ then that is the result for real as I’m going to be shooting this rifle and scope.

or am I being too simplistic?

Not sure on all this worrying about your load or ability to shoot, if either is in question then checking if the scopes working is a complete waste of time - perfect scope + crap shooter/load = crap result anyway

Think I’ll miss by my errors as in poor marksmanship as opposed to a decent scope's possible error?

T

ps if you do not check on a live fire then you have no idea if recoil will mess with the adjustments - just saying

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6 minutes ago, terryh said:

I’ll throw my 5 pence in As this ems to be picking the fly shite out of the pepper

What I Have ‘done’ to check scope ‘installationis use a tallish inverted T target at a short range.

the T is drawn on the already in place target with a spirit level for both the bottom horizontal and vertical line.

Check the rifle’s zeroed on a dot on the target, then by only aiming at the junction of the T and adding good hands full  of elevation shoot rounds up and down the vertical, coming back to the zero of the junction. You then see if the vertical groups matched the settings and the groups tracked up and down the line. This gives you your  actual click value and also if the scope’s on the rifle ‘vertical’.

As this is actual results with the scope and rifle combination ‘as is’ then that is the result for real as I’m going to be shooting this rifle and scope.

or am I being too simplistic?

Not sure on all this worrying about your load or ability to shoot, if either is in question then checking if the scopes working is a complete waste of time - perfect scope + crap shooter/load = crap result anyway

Think I’ll miss by my errors as in poor marksmanship as opposed to a decent scope's possible error?

T

ps if you do not check on a live fire then you have no idea if recoil will mess with the adjustments - just saying

Won't you have already aimed and pulled the trigger before it goes bang ?

Meaning whatever was dialled on the scope should be where the bullet is going as the scope was unaffected by recoil when you aimed at the target 

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34 minutes ago, terryh said:

I’ll throw my 5 pence in As this ems to be picking the fly shite out of the pepper

What I Have ‘done’ to check scope ‘installationis use a tallish inverted T target at a short range.

the T is drawn on the already in place target with a spirit level for both the bottom horizontal and vertical line.

Check the rifle’s zeroed on a dot on the target, then by only aiming at the junction of the T and adding good hands full  of elevation shoot rounds up and down the vertical, coming back to the zero of the junction. You then see if the vertical groups matched the settings and the groups tracked up and down the line. This gives you your  actual click value and also if the scope’s on the rifle ‘vertical’.

As this is actual results with the scope and rifle combination ‘as is’ then that is the result for real as I’m going to be shooting this rifle and scope.

or am I being too simplistic?

Not sure on all this worrying about your load or ability to shoot, if either is in question then checking if the scopes working is a complete waste of time - perfect scope + crap shooter/load = crap result anyway

Think I’ll miss by my errors as in poor marksmanship as opposed to a decent scope's possible error?

T

ps if you do not check on a live fire then you have no idea if recoil will mess with the adjustments - just saying

If you do it with live fire it is not the scope you are checking, it is the scope, rifle, user, bullet, load  combination.

If you want to check if the scope is tracking properly then check just the scope.

If that tracks properly then then add other variables 

 

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Gluv

True if you are ‘assuming’ your scope does not have any slack in it. But concur doing a fixed test should show if you have to do anything funny to achieve constant adjustment or the adjustments are true. You can do this just before you shoot the dam rifle.

Avian

All those variables would have been sorted way before you start checking if the scope is tracking. As I said if you cannot shoot or your rifle throws bullets all over the shop what is the point of worrying about tracking in the scope?

Caveat: if you have no confidence in your scope, (or actually any part of your shooting set up) then you will never do well, so go calibrate your scope however you feel yields the result you want.

Me, I’ll keep doing what I feel happy with and worry about organising more trigger time, bottom line, buy a decent scope and then go and enjoy your shooting :) 

T

 

 

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23 hours ago, brown dog said:

Calibration is the act of empirically assessing the theoretical click value.

Of course it isn't.

Calibration is the act of empirically assessing the ACTUAL click value.  It includes any effects of deficiencies in the theory arising from currently  'unknown unknowns'.  That is one reason why theory and practice diverge.

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Some indivudually brief comments:

Bradders -scope calibration is  a precision issue,you don't have to readit oreven worry about it-good luck with your Precision (22rf?) Rifle ideas..."if I can get it off the ground"- one good way to get any rifle (except a black one-concession,not confrontation) ) off the ground,is to use a bipod (look it up).  

Chanonry,yes thanks for that-of course it is-as I suggested 'theoretical' was a weasel word for Matt to use (my quote of Yogi was just an attempt to lighten the discussion up a bit).

Terry, I think more or less on the same page-and especially wrt to your reply to Avian-all these alleged potential misleading errorsare likely removed prior to a competent shooter doing the firing test. (And see below for some detail).

Gluv...well, read on a bit....

OK.

NO-one has actually given areplicable account of how a non firing scope calibration test would be done. I think it's possible-subject to what follows-but liable to human error (it would take an optomatrist to clarify,let alone measure such error.  I see the rifle with bubble clamped frirmly,and aimed at some  horizontal mark on the paper at a measured distance away (100y- if you prefer,in all of this,substitute metres/mils etc-the principles and proceeduresarethe same).There willl have to be a clear bottom horizontal for the scope crosshair to be aligned with - easy enough. Clicksarethen wound on upwards...lets say 20 moa worth as per scope makers claims...and the cross hairs now aligned with....ah what- a set of very recisely scribed horizontals ? Around the 20 moa elevation area (let say 20-22 inches-but how thick are these lines-they will have to be clearly visible and discerniblefrom each other(acuity) and sufficiently thin seperable to allow fine alignment ( 5% error is unacceptable,so maybe 2% needed to pass the scope as useable.See below what that means,but i'd take 1moa as about an inch at 100y,so .1 means lines separated by only .1 inch....I just don't know if such would be visible enough(or what magnification would do it-quite high,i'd think.)If so,then the proceedure has limited application  to only such scopes.Perhaps someone could obligewith specifics,as I am no expert on visual acuity so assessed.

All this done,of course,the actual vertical produced by the known clicks can be measured,as in the TT test,with similar accuracy of measurement.

A wind on of windage (say 10 moa) for both methods allows the windage calibration-not neccessarily the same as vertical...but of course in the optical no fire it will need some very accurate vertical lines about 9-12 inches to the side.Fire TT just needs a shot/group-no need  for lines.

   OK,please let's have the details of the optical method,dealing with acuity etc .Itseems in principle doable-though I've never seen/reado it being done.

   The basic box test is often done and reported,including by UKV members who test scpes. Basic :fire a shot,click up say 20 moa,fire again,click 20 right (orL) fire a shot,click down 20 moa,fire a shot,and click left (or R) lef 20 and fire a shot-a good tracing scope should allow the first and last shotsto be touching/overlapping.Measuring just what is the actual  distance between appropriate shots gives some measure  for calibration. O course,groups could be shot. But this raises the issue of rig (rifle and ammo precision,and shooter 'accuracy'....indeed,several have  raised this issue...but consider:

 A decent Bench Rest  rig will shoot .25  at 100y,as an aggregate for 25 shots,in standard Diggle conditions (some wind). THe larger component of what is a small dispersion is horizontal(wind induced) but there may be some vertical errorfrom all the alleged raft of possibles.Lets say .1 moa,and that is  under less than very good conditions.I hope it's clear that testing for scope calibrationneeds very good conditions. So all the  alleged errors wil not exceed .1moa. ( accepted some shootersanr rigs  not that consistent-but then such will not do any test so well,and moreover,their real shooting will be confounded by far more error sourcesthan small scope issues). So we have a shooter error under .1 moa....nothing is going to  be perfect (I'm not sure human eyes are that acute for the optical non fire version) a .1 moa  shooter error seemsacceptable in a test wich would be  higjly successful with a 25 calibration error. 5% is too much (with 30 moa up for 1000y shooting,5% error is 1.5moa,about 15 inches (and too much?) but 1% error is only 3 inches-about as good as one might hope for (perfection being zero inches). OK,the thrust of all this is that the TAll Target live fire test is NOT  prone to unacceptable erorof the sort alleged.I doubt that the optical would be either,though differnt issues might arise.

Tall test is  both fuly specified and fit for purpose

.

Checking vertical tracink is a nice bonus (though a less likely mechanical error,hard to otherwise diagnose (as wind blows to the sides too in real field/comp shooting).

Sorry,all this should already be adequate,but  LItz eg is in it's third edition,since 2015 publication-I have never seen any criticism of the Tall Test methodology.The box test is similar enough,and has  been in use longer-again,never seen any criticism.No criticism does not mean immune,just that so far,no-one has in any public way.

   If there are viable alternatives,preferably as human error free,and as practicable-hooray- I'm all for  several measures (if they correlate highly,as they must,if valid)-just as several dictionaries can help with  labels.I'll stick with LItz,but it matters not-the concepts do,and for he is the clearest theoretically,and  useful /pragmatic ,and is explicit about each.He also shoots very well,especially at  very long range,where all this really matters.

One  "refinement",I buy into the clear  distinction between precision (engineering of the rifle and ammo) and accuracy (what the shooter' skill brings to hitting the target)-ignoring/confusing this  is a major source of profound mischief,but I'd see ancilliaries ( rests,triggers and especially scopes here) as engineered hardware that enables the skilled shooter to bring out  more such precision in actual accurate performances.

Sorry it's so long- Saturday indulgence. There is more in Litz (pp432) for them as wants to know,though that includeds maths  and equations-absolutely a virtue where valid (as on 431 pages;-at a pinch I'll add the  dedication one that says ..."and 2+2 is always 4", because were it otherwise, we'd  be in big trouble,up that famous creek,without a bipod ....or 'heaven'  as  Bradders would  construe it.

Your choice,but remember it's a hobby,whether done well,or modally....  :-)

gbal

 

   

 

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