Mil-Dot reticle help pls clever fellas

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09-10-2020, 05:55 PM
Flyblown

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Mil-Dot reticle help pls clever fellas

OK fellas...

I'm having a real "thick" moment. The mil-dot reticle on a 2.5-15x second focal plane scope I am interested in has the specs shown on the attached image. My understanding is that mil-dot scopes are calibrated at 10x magnification to generate the correct holds on the ballistic solver. Milspec says so (I think) and is kind of backed by the fact that for many years military snipers used fixed 10x scopes. (I'm dredging the dark corners of my memory now so may be wrong.)

So in the image, at 15x power, the distance between two dot centres is 2.27 MOA, so 0.66 mrad. If it was calibrated at 15x, then this value should be 3.44 MOA or 1.00 mrad.

Seeing as how we have the values for 2.5x power, how do I calculate the 10x power value to confirm 10x calibration? I am expecting the distance between two dot centres at 10x power to be 3.44 MOA / 1.0 mrad.

Hope this makes sense. Any help that solves this will be much appreciated.
09-10-2020, 06:07 PM
sneeze

If its correct on 10x then 15x makes factor of 1.5 .
3.44 divided by 1.5 = 2.29 so from 15x to 10x it will be x 1.5 or 2.29 x 1.5= 3.44.

1mill /1.5 =.666 so yes looks like its true at 10x
09-10-2020, 06:52 PM
Flyblown

Seems to work the other way as well.... ish.

2.5/10= 0.25
13.46x0.25=3.365

Don't really understand why the numbers we're generating aren't exact.

EG 2.27 vs 2.29 and 3.44 vs 3.365
09-10-2020, 07:02 PM
sneeze

Could be a number of things but Id guess the magnification values on the scope arnt exact. its quite common.
09-10-2020, 07:51 PM
Puffin

Agree – looks like rounding in the published magnification figures.
Calculates to be 2.554x to 15.13x
if the 1mil at 10x is spot on.
09-10-2020, 09:19 PM
Micky Duck

stick your meter ruler up at hundred yards/meters....or paper with known grid size on it....it SHOULD almost make working out whats what too easy....how many inch grids apart are your dots.....how many on each power setting....
D is really the only one you will use is it not???
09-10-2020, 09:35 PM
Woody

There are 91.46 metres at 100 yards. Mils are 19cm at 100 metres. An moa @100m = 1.141"
09-10-2020, 10:26 PM
Feral

Or just go FFP MRAD. Just saying...

Sent from my SM-G980F using Tapatalk
09-10-2020, 10:51 PM
Flyblown

Quote:

Originally Posted by Feral

Or just go FFP MRAD. Just saying...

I’ve got three.

But they aren’t right for this application. Horses for courses and all that.
09-10-2020, 10:53 PM
Flyblown

Quote:

Originally Posted by Woody

There are 91.46 metres at 100 yards. Mils are 19cm at 100 metres. An moa @100m = 1.141"

That’s a typo I assume @Woody. A mil is 10cm at 100m.
09-10-2020, 10:54 PM
Flyblown

Quote:

Originally Posted by Micky Duck

stick your meter ruler up at hundred yards/meters....or paper with known grid size on it....it SHOULD almost make working out whats what too easy....how many inch grids apart are your dots.....how many on each power setting....
D is really the only one you will use is it not???

Only works if you’ve already bought the scope, which I haven’t!
09-10-2020, 11:26 PM
Ftx325

Okay... call me stupid but why have an mrad scope then convert it to moa ? Isn't the whole point of mrad to do away with moa... I thought mrad was supposed to be easier to use. Sure as hell don't look like it if you need to recalculate everything across from moa. And shouldn't the scope manual tell you which magnification is correct for 1mil at 100 mtr. Call me old school but I will stick to moa thanks....ok , rant over
10-10-2020, 07:51 AM
Cordite

Mil dot range finding.
…..................................

A full circle of 360degrees is 6283milliradians, or mils.

1mil @ 100m = 10cm
1mil @ 200m = 20cm
1mil @ 300m = 30cm
1mil @ 400m = 40cm
.
.
1mil @ 1000m = 100cm
1mil @ 1800m = 180cm

Quick calc, memorise this:

Height in cm / measured height in mils = distance in metres.

With the above you can determine at which precise setting your mil dot reticle actially measures mils.

And boys, lets forget about yards and inches.
10-10-2020, 07:59 AM
Ftx325

Quote:

Originally Posted by Cordite

Mil dot range finding.
…..................................

A full circle of 360degrees is 6283milliradians, or mils.

1mil @ 100m = 10cm
1mil @ 200m = 20cm
1mil @ 300m = 30cm
1mil @ 400m = 40cm
.
.
1mil @ 1000m = 100cm
1mil @ 1800m = 180cm

Quick calc, memorise this:

Height in cm / measured height in mils = distance in metres.

With the above you can determine at which precise setting your mil dot reticle actially measures mils.

And boys, lets forget about yards and inches.

I think the problem is he doesn't actually have the scope to test it out on a target to confirm those measurements on the reticule the easy way. Hence the nasa/particle physics level mathematics equations.
10-10-2020, 08:43 AM
Cordite

Quote:

Originally Posted by Ftx325

I think the problem is he doesn't actually have the scope to test it out on a target to confirm those measurements on the reticule the easy way. Hence the nasa/particle physics level mathematics equations.

Yep. I just reckon Flyblown will trust his own measurements more than some factory blurb. So when he gets his scope he will just put a 10cm high or wide target up at 100m and zoom his scope till it coincides with one dot centre to dot centre measurement.

In the end, even if the factory leaflet is accurate, will the graduations printed on the scope zoom ring be correct? Literally only one way to know.

And forget MOA too.
10-10-2020, 08:50 AM
Woody

Quote:

Originally Posted by Flyblown

That’s a typo I assume @Woody. A mil is 10cm at 100m.

Yep.Mil is 10cm @100m. Less at 100 yards.
10-10-2020, 09:19 AM
Flyblown

Quote:

Originally Posted by Ftx325

Okay... call me stupid but why have an mrad scope then convert it to moa ? Isn't the whole point of mrad to do away with moa... I thought mrad was supposed to be easier to use. Sure as hell don't look like it if you need to recalculate everything across from moa. And shouldn't the scope manual tell you which magnification is correct for 1mil at 100 mtr. Call me old school but I will stick to moa thanks....ok , rant over

It’s normal to have a mildot reticle with MOA adjustments on the turret. It comes from the original USMC sniper rifles with Unertl fixed 10x scopes.

In this instance it doesn’t bother me in the slightest what the units the turret is in, because it is not a ballistic turret and generally I will not be dialling up with it. I want the mildot reticle because it aligns perfectly with my .308 ballistics at a 200 meter zero for simple holdover reference points. The dots correspond to 300m, 400m, 475m, 550m. I won’t be using the reticle for ranging purposes because I’ve got a rangefinder for that. So no calculators involved!

If I was to take the cap off the turret and dial up for a particular shot, which might happen from time to time, then to get past the units problem I have learnt to work in “clicks”.

This particular reticle has an illuminated centre dot which works extremely well from what I saw this week thanks to one of our helpful forum members, @johnd. Thanks again mate. The only outstanding question was the calibration magnification and I am expecting that to be 10x, thanks for the confirmation of this fellas. Once the scope is here and set up then I will do the paper on the post exercise, and determine precisely where on the magnification ring the centre dot to centre dot distance corresponds to 10cm at 100m.
10-10-2020, 09:40 AM
Marty Henry

I had a clear Ridge mil dot 2nd focal plane, the 10x on the zoom ring was red which was
clever idea and a bit of a give away for the correct magnification.
10-10-2020, 10:23 AM
grandpamac

Greetings All,
Probably a good time to remind everyone that a mil and a milliradian (mrad) are two different units. Our American cousins routinely get the two scrambled. A mrad works out to 10 cm at 100 metres exactly and a mil is 9.8cm. Smaller than the difference between 1MoA and 1 inch at 100 yards yes but different just the same.
Regards Grandpamac.
10-10-2020, 12:52 PM
zimmer

Just to confuse..

Definitions of the angular mil

There are 2000π milliradians (≈ 6283.185 mrad) in a circle; thus a milliradian is just under 1⁄6283 of a circle, or ≈ 3.438 minutes of arc. Each of the definitions of the angular mil are similar to that value but are easier to divide into many parts.

1⁄6400 of a circle in NATO countries.
1⁄6283 The “real” trigonometric unit of angular measurement of a circle in use by telescopic sight manufacturers using (stadiametric) rangefinding in reticles.
1⁄6000 of a circle in the former Soviet Union and Finland (Finland phasing out the standard in favour of the NATO standard).
1⁄6300 of a circle in Sweden. The Swedish term for this is streck, literally "line". Sweden (and Finland) have not been part of NATO nor the Warsaw Pact. Note however that Sweden has changed its map grid systems and angular measurement to those used by NATO, so the "streck" measurement is obsolete.
10-10-2020, 01:16 PM
grandpamac

Thanks Zimmer,
I believe that the US armed forces used two different versions at the same time between the wars.
Regards Grandpamac.
10-10-2020, 02:59 PM
Flyblown

I realise just how thick I was being yesterday, not just with the primary level maths but also how to use Strelok to solve this problem easily. I blame it on the meds... and the kids... and the dogs... Using the values provided by the scope manufacturer I can clearly see how a 10 times calibration produces the 15x and 2.5x MOA values.

I’ve also been able to work out that this reticle is based on the US Army version of the mildot, not the US Marine Corps. Doesn’t make any practical difference to the holds in the field though.