mil dot vs mil rad

[roval]

i'm getting confused. i'v always understood that mildots are representative of 1 milrad between the dots(center to center). but a gun shop employee who was supposedly ex army sniper glibly said milrads are not the same as the distance between mildots. i've read that the military rounded off a circle to 6400 mils instead of 6175 for ease of computation( plaster, ultimate sniper) but i don't think this was what he meant. when i asked him what he meant he just shrugged and said they were not the same. this was in the context of me looking at a scope with hash mark milrad reticle instead of mildots. (it was a mil mil scope(vortex pst) so he wasn't talking about the adjustments). i've brushed it off but then i asked another employee some other time if was truly ex sniper and he confirmed so I asked him the same question and he agreed that they were different but couldn't explain. were they just full of it or am i misunderstanding something.

 

[MCMXI]

i'v always understood that mildots are representative of 1 milrad between the dots(center to center).

This is correct for quality front focal plane scopes at any magnification and quality second focal plane scopes at a specific magnification. The "ex sniper" might be confused since the military hasn't always used front focal plane scopes.

 

[roval]

thanks but i still couldn't imagine what he may be referring to. i'm sure they get drilled in this thoroughly even before they went to the range, range estimation etc...

 

[Outlaw Man]

There are also lots of "ex army snipers" out there.

1858 is correct. They are the same, under those circumstances.

Now, as a technicality, the distance between dots isn't a mil, since the dots generally have a thickness (0.2 mil, for instance). The distance, center-to-center, is a miliradian, though. Maaaayyybe that's where he was getting confused.

 

[MCMXI]

ex army sniper glibly said milrads are not the same as the distance between mildots

i still couldn't imagine what he may be referring to

Does it matter? He didn't bother to explain his comment so look at the images from Leupold below and make up your own mind as to whether he's correct or not.

i've read that the military rounded off a circle to 6400 mils instead of 6175 for ease of computation

There are 2PI radians in a circle which is 6.283186 radians to six decimal places which is 6,283 milliradians as a whole number. I'm not sure where you get 6175 from.

 

[Robert101]

1858, great response. That picture says it all. I've saved it for my future reference. Thanks.

 

[roval]

I got it from the book I referenced next to the figure.

 

[CSC_Saint]

he's probably having a brain fart and thinking that because he has to convert to moa from mil readings to make adjustments that they're different. Remember, Army has used Leupold M3A scopes with mil reticle and moa adjustments on the M24 and Leupold's MK4 adjustable mag scopes with the same setup. So anytime you use the mil reticle you gotta convert to moa for adjustment. At least that's how I see it if the guy was making an honest mistake. I can only imagine how much these old sniper guys forget over the years, as I use to know the formula for taking mil readings for range estimation and converting to meters by heart. Three years since I've needed to know it, and it seems like my brain has conveniently dumped that info into a deep dark hole.

 

[roval]

He's a really nice and funny guy and I was going to ask him about his wind dope formula, maybe it was shorter than the formula you see often or how to adjust the formula for other than 308 but after that I just kept quiet. This actually happened quite a while ago. he moved to another shop but I saw the other guy he used to work with at another gun shop I was checking out a few days ago and he's the other one that said the same thing.

 

[Hacker15E]

Great thread!

I find that a lot of shooters get mils and MOA frequently jumbled up, too.

 

[hunttheevil]

The mildot scale was created using the milliradian calculation. Basically, a milliradian is 1/6283 of circle which equates to 3.423 inches at 100 meters. The USMC used 1/6400 given circle to develop the 3.6 inch mildot measurement at 100 meters in the 1970's, to reduce calculation errors in the field.
3.6 inches at 100 meters is 36 inches at 1000 meters. So an average man 2 mils tall is 1000 meters away, 4 mils - 500 meters, 8 mils - 250 meters.
During WWI the French changed from degrees-minutes to 1/6000 milliradian for their artillery calculations. I believe its the Swiss who use 1/3000 milliradian for their "streck" unit of measure.

 

[roval]

Man I love the knowledge you get from THR thanks

 

[cowtownup]

Great thread... Great reference picture also...

 

[1911 guy]

Yeah, Mils are not always Mils. Artillery uses the "correct" 3.4-something"@100m, USMC and therefore Navy also uses 3.6"@100m. No idea what Army uses and several countries, as mentioned by huntthedevil, have further mashed up the measure and adopted it to several uses, variations and divisions.

 

[MCMXI]

Basically, a milliradian is 1/6283 of circle which equates to 3.423 inches at 100 meters. The USMC used 1/6400 given circle to develop the 3.6 inch mildot measurement at 100 meters in the 1970's, to reduce calculation errors in the field.
3.6 inches at 100 meters is 36 inches at 1000 meters. So an average man 2 mils tall is 1000 meters away, 4 mils - 500 meters, 8 mils - 250 meters.

I don't get any of that. 1 milliradian subtends 3.600" at 100 yards and 3.937" at 100m. The USMC method makes no sense either. If 1 milliradian converted to degrees is 360/6283 (which is correct), how do you end up with 3.6" at 100m by dividing 360/6400? I get 3.865" at 100m using the USMC method.

 

[hunttheevil]

There are 2π × 1000 milliradians (≈ 6283.185 mrad) in a circle. So a trigonometric milliradian is just under 1⁄6283 of a circle. This “real” trigonometric unit of angular measurement of a circle is in use by telescopic sight manufacturers using (stadiametric) rangefinding in reticles. The divergence of laser beams is also usually measured in milliradians.
An approximation of the trigonometric milliradian (0.001 rad), known as the (angular) mil, is used by NATO and other military organizations in gunnery and targeting. Each angular mil represents 1⁄6400 of a circle and is 1-⅞% smaller than the trigonometric milliradian. For the small angles typically found in targeting work, the convenience of using the number 6400 in calculation outweighs the small mathematical errors it introduces. In the past, other gunnery systems have used different approximations to 1⁄2000π; for example Sweden used the 1⁄6300 streck and the USSR used 1⁄6000. Being based on the milliradian, the NATO mil subtends roughly 1 m at a range of 1000 m (at such small angles, the curvature is negligible).

Basically 1/6283 of a circle is the true trigonometric milliradian and 1/6400 of a circle is angular milliradian calculated to achieve the 3.6 inch mildot. 1/x can be used to calculated any mrad to fit your needs.

 

[Caliper_Mi]

The 6400 mils in a circle comes from artillery. See the 2nd paragraph under "history" https://en.wikipedia.org/wiki/Angular_mil

If we are talking milliradians (mrad, or 1/1000 radian), one mrad = 3.44 MOA. Always has and always will. It's an angle so this is regardless of distance. This is talking TRUE MOA though, not the 1" approximation we commonly use.

One mrad also equals 3.6" at 100yd because 100yd = 3600" and 3600"/1000 = 3.6". Many round this off to 1 mrad = 3.6 "MOA", but that's "shooters MOA", not real MOA.

At 100m, 1 mrad = 10cm. Why is everyone thinking of "inches @ x meters" and trying to intermix english and metric... It's like cats and dogs living together!

How scopes are marked will depend on the manufacturer. Best to check with them and then verify at the range with a known size target at a known distance.

 

[hunttheevil]

The 6400 mils in a circle comes from artillery. See the 2nd paragraph under "history" https://en.wikipedia.org/wiki/Angular_mil

If we are talking milliradians (mrad, or 1/1000 radian), one mrad = 3.44 MOA. Always has and always will. It's an angle so this is regardless of distance. This is talking TRUE MOA though, not the 1" approximation we commonly use.

One mrad also equals 3.6" at 100yd because 100yd = 3600" and 3600"/1000 = 3.6". Many round this off to 1 mrad = 3.6 "MOA", but that's "shooters MOA", not real MOA.

At 100m, 1 mrad = 10cm. Why is everyone thinking of "inches @ x meters" and trying to intermix english and metric... It's like cats and dogs living together!

How scopes are marked will depend on the manufacturer. Best to check with them and then verify at the range with a known size target at a known distance.

Yes, I stand corrected and apologize to 1858. After a little research all rifle scope manufacturer's are using 6283. I should have done more research than quote data that was drilled in my head 30 years ago. The short answer to the OP's question (LOL), mildot measurements are the same as mrad. The guy at the gun shop needs re-training now that i'm caught up!

 

[John3921]

The 6400 mils in a circle comes from artillery. See the 2nd paragraph under "history" https://en.wikipedia.org/wiki/Angular_mil


One mrad also equals 3.6" at 100yd because 100yd = 3600" and 3600"/1000 = 3.6". Many round this off to 1 mrad = 3.6 "MOA", but that's "shooters MOA", not real MOA.

I'm not following this description. Millirad is an angular measurement.

There are 2 PI * 1000 millirads in a complete circle.

At 100 yds the radius of said circle is 3600 inches. The circumference of the circle then is: 2*PI*r

So dividing the circumference by the number of millirads = 1 mil

(2*PI*r)/(2*PI*1000) = r/1000 = 3600/1000 = 3.6"

 

[hunttheevil]

Man have I started a crap storm! I'll be back in a week.

 

[Caliper_Mi]

I'm not following this description. Millirad is an angular measurement.

There are 2 PI * 1000 millirads in a complete circle.

At 100 yds the radius of said circle is 3600 inches. The circumference of the circle then is: 2*PI*r

So dividing the circumference by the number of millirads = 1 mil

(2*PI*r)/(2*PI*1000) = r/1000 = 3600/1000 = 3.6"

Another definition of a radian is that it is an angle such that the length of the section of the circle inside the angle is equal to the radius of the circle. (thus 2 Pi radians in the total circle)

Based on that, a milliradian is an angle such that the section of the circle inside the angle is 1/1000th the radius of the circle. Because we are dealing with a very small part of a very big circle, that section of arc is very nearly straight and we can ignore the difference (we really can, the difference is 150 nano-inches at 100yd).

This is where mrad is easy for ranging. Because of the definition of the radian, we don't have to go around calculating equations with Pi in our head. The height of an object that is 1 mrad is 1/1000th the distance to the object. Or, 1 mrad @ 1000yd = 1yd. A 6 foot (2 yd) tall person at 1000yd will be 2 mrad, and so on. If you start trying different scenarios, you'll see that for oddball distances mrad really is easier to work using the metric system, but that's a different discussion.

 

[CharlieDeltaJuliet]

Caliper_RWVA and 1858 hit it right on the head. I started out with MOA, but switched to MIL/MIL since I don't shoot F-Class. I live the easy calculations and ranging.

 

[sscoyote]

For practical useable purposes the true beauty of the milliradian lies not in the angle itself, but in the fact that the mil-ranging formula can be adapted to any subtension, from the mil-dot to simple plex reticles, BDC reticles, and even archery sight pins--really any 2 points at one distance relative to any 2 points at another distance. Here's a youtube I did on that concept--

http://www.youtube.com/watch?v=iNvJKBOpj08

 

[12many]

I am no expert there, but using inches with Mils is the wrong path. Makes my head spin, and I love math.

Use inches with MOA
meter/centimeters with MIL.

2.5 CM per inch, 1 yard is about 1 meter. About . . .

That IMO, makes it easier.

Since I grew up with inches, (although I use metrics for work), I like a scope with MOA knobs, MOA reticles, and knowing the size of stuff in inches. I do have a scope in Mils so will try to work in metric.

 

[itsa pain]

I don't get any of that. 1 milliradian subtends 3.600" at 100 yards and 3.937" at 100m. The USMC method makes no sense either. If 1 milliradian converted to degrees is 360/6283 (which is correct), how do you end up with 3.6" at 100m by dividing 360/6400? I get 3.865" at 100m using the USMC method.

You are right it is a pile of confusing garbage. Should have did it in inches. Why does the military use the metric system for yardage anyway? Adds more confusion