GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Optics, Range estimation & related subjects => Topic started by: Pandur_HR on February 12, 2019, 04:02:51 PM
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Recently I checked Hawke mil-dot rectile (20×1/2) accuracy. I noticed that my POI is always slightly lower.
Hawke Sidewinder 30 6.5-20x42 Tactical IR
So I placed target on 10.2 m from scope. Messured by professional Bosch laser distance meter. Double checked by range finder. Meassured target from center to edge by caliper. 58 mm.
Rectile is calibrated at 20x zoom. So I placed on 20x zoom, adjust paralax and messured 5.2 mrad from center to edge. And it should be about 5.7 mrad.
By Hawke rectile distance is 11.2 m.
If you put that as 11.2 yards and convert to meters, you will get 10.2 m, wich is correct.
Hawke misplaced yards and meters. At least on my scope.
Mistake is 5 cm at 100m.
So what I do now, during zeroing with + scope offset, is decrease the +mrad value by 0.9122 (multiply by that value) or increase the -mrad value by 1.096 then it is correct, and don't shoot lower.
Anyone else noticed that on your Hawke scopes?
Or mine is with error.
Actually, I would not even notice this if I didn't place scope in 25 MOA offset for long range shooting, and try to zero on 25 MOA offset. That would keep the target centered while scope remains in optical center.
25 MOA is 7.2 mrad. Mistake is 7 cm at 100m, or 1.7 cm on 25m. So 0.6 inch at 27 yards. That is how I noticed something is wrong.
More mrad you go, mistake increases. At 1 mrad would be only 2 mm or 0.07 inches. About 7-8 mm on 100m.
But on 7 mrad, that is 0.7 mrad mistake on zero. That is not small anymore.
If my scope is not with error, meaning that other are same. This is big issue for Hawke.
I checked the click value in a same time. 0.253 MOA, that is OK.
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The reticle is likely fine.
The discrepancy can come from several places. And it applies to all scopes, not just Hawkes.
1st question is where are you taking the distance reading from?
I take my readings from the second focal plane, which is near the erector tube gimble. The magnification ring on the scope is a good external reference for measuring distance to the target. If you do that, you might get closer to the expected value when measuring close targets.
Also, the markings on the magnification ring are often inaccurate.
Adjust the magnification until you get the dot spacing that you want, and then mark that location on the ring.
For me, I don't worry if the dot spacing is exactly a milliradian. I usually make up a dope sheet specific to each scope at the magnification that I prefer to shoot at. That makes exact milliradians irrelevant.
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Sounds like zoom ring slop.
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Sounds like zoom ring slop.
Could be.
What I found intetesting is that 1 meter matching 1 yard.
So when you take a results as yards and convert back to meters everything is OK.
Mrad is a metric value, it don't messure yards.
Might be coincedence. Might not.
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The reticle is likely fine.
The discrepancy can come from several places. And it applies to all scopes, not just Hawkes.
1st question is where are you taking the distance reading from?
I take my readings from the second focal plane, which is near the erector tube gimble. The magnification ring on the scope is a good external reference for measuring distance to the target. If you do that, you might get closer to the expected value when measuring close targets.
Also, the markings on the magnification ring are often inaccurate.
Adjust the magnification until you get the dot spacing that you want, and then mark that location on the ring.
For me, I don't worry if the dot spacing is exactly a milliradian. I usually make up a dope sheet specific to each scope at the magnification that I prefer to shoot at. That makes exact milliradians irrelevant.
Distance had been messured by this tool.
https://www.boschtools.com/us/en/boschtools-ocs/laser-measuring-glm-50-35087-p/ (https://www.boschtools.com/us/en/boschtools-ocs/laser-measuring-glm-50-35087-p/)
Werified by range finder and building drawing.
https://www.hawkeoptics.com/laser-range-finder-pro-400.html (https://www.hawkeoptics.com/laser-range-finder-pro-400.html)
Target had been messured by a caliper.
https://upload.wikimedia.org/wikipedia/commons/f/f6/Vernier_caliper.svg (https://upload.wikimedia.org/wikipedia/commons/f/f6/Vernier_caliper.svg)
0.058 m height at 10.2 m. That is 5.7 mrad.
Hawke rectile is calibrated at 20x zoom. My max zoom is 20x. So I put it on max.
Adjust the paralax and messured 5.2 mrad.
0.5 mrad mistake.
Scope is:
https://www.hawkeoptics.com/sidewinder-65-20x42-20x-mil-dot.html (https://www.hawkeoptics.com/sidewinder-65-20x42-20x-mil-dot.html)
I am zeroing scope at 6.2 mrad up. So I have 0.6 mrad error. Gun shoot for that value lower.
1/2 inch at 25 yd
1 inch at 50 yd
2 inch at 100 yd.
If I take meters as yards, and convert back, everything is OK.
It can be coincedence. But this is a wierd coincedence.
This is extremly hard to notice when you zero scope at crosshair, 0 mrad. And don't shoot below -2 mil.
On -2 mil error is 0.17 mrad.
Slightly above 1/2 inch at 100 yd.
1/8 inch at 25 yd.
1/4 inch at 50 yd
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Actually, even earlier I noticed that I regulary shoot slightly higher then calculated on long range. I always tought that is an error from ballistic calculator.
Now I now it was not, rectile is miscalibrated.
When you zero scope on 0 or on minus mrad. Then gun will shoot higher at longe range. Opposite from zeroing the scope at +mrad.
9% mistake.
Coincedence or not, this is nasty error.
For those not familiar with a metric system.
0.6 mrad is about 2 moa or 8 clicks with 1/4 moa turrets.
That is half space beteeen 2 mil dots at rectile. Or one 1/2 mil dot at hawke rectile.
That is not small.
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Some people take range distances to the muzzle. That's correct for calculating drop. But it is incorrect for calculating reticle distance. The scope does not know how long the barrel is. A pistol is very different than a rifle. It sometimes makes a difference of over 1/2 yard.
Some people assume to the objective, but that is not quite right either. For long distances, it makes little difference. But as the distance gets closer, measurement errors become more obvious.
I'll ask again - where are you measuring to? Target to muzzle? Target to objective? Or target to gimble?
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Mrad is a metric value, it don't messure yards.
A Milliradian (MRad) is an measure of angle, it is neither Metric nor Imperial measure.... It is by definition 1/1000 of a radian, which is the angle where the length of arc equals the radius.... One MRad is therefore 1/1000th of the distance to the target.... That could be 1 metre at 1000 metres, 1 yard at 1000 yards, 1/10th of a yard (ie 3.6") at 100 yards, or 1/10th of a metre (10 cm) at 100 metres…. It would also be 1 cm at 10 metres, etc.etc.etc….
Bob
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Mrad is a metric value, it don't messure yards.
A Milliradian (MRad) is an measure of angle, it is neither Metric nor Imperial measure.... It is by definition 1/1000 of a radian, which is the angle where the length of arc equals the radius.... One MRad is therefore 1/1000th of the distance to the target.... That could be 1 metre at 1000 metres, 1 yard at 1000 yards, 1/10th of a yard (ie 3.6") at 100 yards, or 1/10th of a metre (10 cm) at 100 metres…. It would also be 1 cm at 10 metres, etc.etc.etc….
Bob
That is true Bob.
What I ment was, that when it comest to scopes it is commonly used as 10cm on 100m value..
Amyway, one I have is not 1/1000 of yd either.
It look as 0.1yd/100m.
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I will not warranty it. Math to correct it is very simple.
It can be taken as 10%, trivial to calculate. 3 mrad corrected at 2.7 mrad as example. 1% on my distances are very small values.
I only wonder is my with a mistake, or this is design failure.
Sidewinder tactical series are all caliber rated. They already offer too much for a value they are sold. Great value for a money spent. All caliber rated scopes in that price category offer less then Hawke.
Perfection cost few thousands USD in a category sidewinder tactical is. But it cannot but put on a magnum springer air rifle :-) Hawke offer even that. :-)
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I will not warranty it. Math to correct it is very simple.
It can be taken as 10%, trivial to calculate. 3 mrad corrected at 2.7 mrad as example. 1% on my distances are very small values.
I only wonder is my with a mistake, or this is design failure.
Sidewinder tactical series are all caliber rated. They already offer too much for a value they are sold. Great value for a money spent. All caliber rated scopes in that price category offer less then Hawke.
Perfection cost few thousands USD in a category sidewinder tactical is. But it cannot but put on a magnum springer air rifle :-) Hawke offer even that. :-)
You said your distance was 10.2m.
You never answered where you held your range finder or meter when taking the distance readings. If you held them back by the scope eyepiece, you did it right. But if you were near the muzzle, the actual reticle distance to target would probably be closer to 11m.
Target measured 58mm (.058m).
0.058m/11m x 1000 mrad/m = 5.27 mrad
That's not far off from the 5.2 mrad that you said you measured. That's less than a 2% error, which agrees better than half of the scopes that I own.
If you are going for that level of precision when calibrating your reticle, a tape measure would be better than a laser range finder. And use a target that spans 10mrad. That will reduce the rounding errors and give you a more precise % error calculation.
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I messured from front lense, from back lense is 10.6 m, 5.45 mrad.
O.25 mrad error at 5.45 mrad is 5% error. That is tolerable on my distances, and not hard to correct. Submoa accuracy is OK. 0.25 mrad = 0.85 MOA. On 7 mrad (top of rectile) would be about 0.35 mrad or 1.2 MOA, for me still OK.
Anyway, it is not 1 yard for 1 meter anymore. Glad to find that out. :-) That would be a huge design mistake.
Thank you for help Scott.
PS
That Bosch tool is something I use for work, not for shooting. It was compared against messuring tape multiple times. Incredibly accurate tool.
Exact values. 10.23m and and 10.62m
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BTW I compared Hawke range finder against the same tool and known distances. Hawke range finder messure correct. As declared +- 1m for me OK.
Paralax marking on scope is almost full correct. :-) But OK, this is influenced by a temperature. And Hawke clearly mentioning those values are for orientation only.
As I said, great value for money.
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Why am I checking this. I am trying to place airgun ELR shot. Meaning I will have scope zeroed on top of rectile and target will be on bottom.
Previously I calculated almost 5 MOA error. That is larger then the target. I cannot hit it. Now (after messuring error is corrected) I have 2.4 MOA, that is OK.
Larger problem is ballistics and ES (I am still struggling with this one). And the largest of all - springer with a slow twist rate. :-)
Chances are very low for success, but why not try. :-)
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You are checking the dot spacing at close range. But if you intend to use the scope at longer distances, you should check the dot spacing there. Especially on SFP scopes, the apparent magnification changes slightly as you move the focus adjustment. There is a good chance that small error will be even less at 30m.
When comparing 10yds to 30yds, a 5% variation in the angle between dots is fairly common.
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Thank you on advices Scott.
Yes, I will recheck all at the target distance.