MRAD vs. inches vs. MOA

[338 dude]

My head hurts I'm going to look at another post!

 

[Tangent]

An angle is two rays sharing a common vertex.

Any specific angle is defined by that angle's arc of subtention.

It is the arc that defines the angle, or the angle wouldn't exist.

That is incorrect.

Here is an angle <

there isn't an arc, but there is an angle.

Triangles don't have arcs, but they do have angles...so do squares, so do pentagons, etc., etc., etc.

Arcs are not angles.

 

[Richard of Oz]

Your confusing two concepts. An arc is a portion of a circumference. Angles and arcs are related as follows:

S = R*Theta where S is the arc length, R is the radius, and theta is the angle.

The reason there are 2*PI radians in a circle is because pi is the ratio of circumference divided by diameter (this is true for all circles).

pi = C/D

A radius is 1/2 the diameter, so rearrange:

pi = C/(2R)

2*pi = C/R (this is also always true for every circle)

Combine these two aforementioned concepts to understand the following:

A radian is defined as the angle that subtends an arc that has the same length as the radius.

Yes, quite right, the radian is the angle, not the arc subtended by that angle. But though that's technically correct, it's relevant only to the math purists here. For practical purposes, the important point is the 1:1000 relationship between mils and radius (or range), as it is both accurate and easy to remember, unlike all other so-called explanations and formulas which I've seen.

 

[Ranger Rick]

Simple intro: 1 MOA is 1/60 of a degree In a 360 degree circle. Just compare time, one minute is 1/60 of an hour. From the muzzle, the angle increases as the distance increases. Hence the "distance" from the muzzle makes the angle open up. For rounding, which works ok for many distances, 1 MOA is ~ 1" at 100 yards, 2" at 200 yards ... 12" at 1,200 yards. Precisely 1 MOA = 1.047" per 100 yards. At 1,200 yards the difference between the the rounded number 1" and the precise number 1.047" is only 0.56". The key factor in MOA or mils is knowing the distance. PTL for rangefinders. At 1,200 yards, rounded MOA is 425/12 = 35.4 MOA up. At precise, 425/12.56 = 33.84 MOA. There are two answers. But ram rock gets my vote for tactfulness.

 

[Tangent]

Simple intro: 1 MOA is 1/60 of a degree In a 360 degree circle. Just compare time, one minute is 1/60 of an hour. From the muzzle, the angle increases as the distance increases. Hence the "distance" from the muzzle makes the angle open up. For rounding, which works ok for many distances, 1 MOA is ~ 1" at 100 yards, 2" at 200 yards ... 12" at 1,200 yards. Precisely 1 MOA = 1.047" per 100 yards. At 1,200 yards the difference between the the rounded number 1" and the precise number 1.047" is only 0.56". The key factor in MOA or mils is knowing the distance. PTL for rangefinders. At 1,200 yards, rounded MOA is 425/12 = 35.4 MOA up. At precise, 425/12.56 = 33.84 MOA. There are two answers. The deer is dead either way. I will leave mils for the GIs.

How big of deer do you shoot, haha. I'll go out on a limb and guess you don't shoot 1,200 yards too often. A 20" error is a major mistake.

 

[7magcreedmoor]

Simple intro: 1 MOA is 1/60 of a degree In a 360 degree circle. Just compare time, one minute is 1/60 of an hour. From the muzzle, the angle increases as the distance increases. Hence the "distance" from the muzzle makes the angle open up. For rounding, which works ok for many distances, 1 MOA is ~ 1" at 100 yards, 2" at 200 yards ... 12" at 1,200 yards. Precisely 1 MOA = 1.047" per 100 yards. At 1,200 yards the difference between the the rounded number 1" and the precise number 1.047" is only 0.56". The key factor in MOA or mils is knowing the distance. PTL for rangefinders. At 1,200 yards, rounded MOA is 425/12 = 35.4 MOA up. At precise, 425/12.56 = 33.84 MOA. There are two answers. The deer is dead either way. I will leave mils for the GIs.

The problem with rounding is when you get far enough out, the deer isn't dead either way. When you need to dial up 33 to 35 of them, rounded MOA aren't the same as true MOA by ~19 inches. That's a miss on most deer.

 

[7magcreedmoor]

Reticle ranging using rounded minutes: 72 inch tall target divided by 6 observed minutes = 1200 yards. My 280AI needs 29.75 MOA up for that distance.
Reticle ranging using true MOA: 72 inch tall target divided by 6 observed minutes =1146 yards. Same rifle and load needs 27.5 up for actual distance.
IF I use rounded minutes, I shoot over my intended point of impact by almost 27 inches.

 

[Richard of Oz]

Simple intro: 1 MOA is 1/60 of a degree In a 360 degree circle. Just compare time, one minute is 1/60 of an hour. From the muzzle, the angle increases as the distance increases. Hence the "distance" from the muzzle makes the angle open up. For rounding, which works ok for many distances, 1 MOA is ~ 1" at 100 yards, 2" at 200 yards ... 12" at 1,200 yards. Precisely 1 MOA = 1.047" per 100 yards. At 1,200 yards the difference between the the rounded number 1" and the precise number 1.047" is only 0.56". The key factor in MOA or mils is knowing the distance. PTL for rangefinders. At 1,200 yards, rounded MOA is 425/12 = 35.4 MOA up. At precise, 425/12.56 = 33.84 MOA. There are two answers. The deer is dead either way. I will leave mils for the GIs.

That deer is not dead, mate, he's laughing at you from the next county! He'd have to be one BIG deer to have a vital zone just under 20 inches tall, and to kill him you'll need a gun way bigger than whatever you have now.
Don't leave mils for the GIs, just learn how simple mils are and make life simple for yourself. 1 mil is just your range (in inches, yards, meters, or whatever) divided by 1000...So 1 mil at 1200 yards (43,200 inches) is 43.2 inches, and your required correction of 425 inches is 9.84 mils... Pretty simple!

 

[Richard of Oz]

Reticle ranging using rounded minutes: 72 inch tall target divided by 6 observed minutes = 1200 yards. My 280AI needs 29.75 MOA up for that distance.
Reticle ranging using true MOA: 72 inch tall target divided by 6 observed minutes =1146 yards. Same rifle and load needs 27.5 up for actual distance.
IF I use rounded minutes, I shoot over my intended point of impact by almost 27 inches.

The trouble with using either mils or moa for ranging is that, though the concept is simple, it isn't easy to get an accurate measure of mils/moa on a target, particulartly if it's moving or atmosheric conditions are poor. At extended ranges your propjectile can be dropping like a stone, and a small error in estimation is a miss.

 

[7magcreedmoor]

The trouble with using either mils or moa for ranging is that, though the concept is simple, it isn't easy to get an accurate measure of mils/moa on a target, particulartly if it's moving or atmosheric conditions are poor. At extended ranges your propjectile can be dropping like a stone, and a small error in estimation is a miss.

Absolutely! You have to have a rock solid rifle support to see well enough in the first place, then mirage etc will mess with you, then there is the challenge of discriminating the reticle subtensions with sufficient accuracy, angle-to-target affecting perceived size, actual knowledge of target size (except steel you hung out there yourself). I only gave the example to further illustrate the perils of rounding. I use my trusty old G7BR2. Unless I can't because of atmospherics, or dead battery, or I can't get a good bounce off the target or something near it. Basically there is a lot that can screw up a long shot. The loose nut on the trigger being foremost...

 

[Richard of Oz]

Oh, man! Please, a little more respect here! Remember that this forum is for members to ask questions and get help from other members. It is not a vehicle for members to slag off on each other.
I always find that the whole subject of mils and moa is very poorly understood by the shooting community. Even the many "expert" videos on the subject do more to confuse than enlighten.
First, understand that a mil, or milliradian, is by definition a thousandth part of a radian. And a radian is an arc (or part of a circle) whose length is equal to the radius. So at a range (or radius) of 100 yards (3600 inches), 1 mil = 3.6 inches EXACTLY. And at 100 meters, 1 mil = 10 cm EXACTLY. To revert to the original example, there are 43,200 inches in 1200 yards, so at that distance 1 mil = 43.2 inches EXACTLY. And a correction of 425 inches is therefore 425 / 43.2 = 9.838 mils. Note that the value derived by TANGENT using the arctan trig function is ever so slightly different from this because we're dealing with spherical measurements here rather than perfect triangles. But at this level of precision we are stepping out of the real world and into the world of mathematical fantasy, for shooting purposes. So let 9.8 mils stand.
Just keep this 1:1000 relationship in mind and forget all the other formulas you've ever heard on the subject of mils.
Second, understand that the common use of 1 moa = 1 inch at 100 yards is an APPROXIMATION for convenience in the field. For practical purposes the approximation is useful and sufficiently accurate. A more precise value is 1.0476 inch, but let's not get anal here. For precise calculations, you need to be aware that the error of 0.05 inch per 100 yards may accumulate to something significant when you're shooting past your back fence. (My back fence is a long way out.)
Again, please mind your manners, folks. Trolls aren't welcome, and no one likes a wise guy.

Ha ha! What I actually wrote at the end was not "wise guy", but "s****a**", but I forget that Americans have very tender sensibilities. Dear oh dear, Mr Moderator, is that really necessary? Are our members really so innocent? How 'bout it, guys?
What a hoot! B***** h***!!!

 

[Len Backus]

Richard.

I make the rules and I enforce them.

You have a choice, there are many other forum sites on the net that will allow crude language.

 

[Ranger Rick]

How big of deer do you shoot, haha. I'll go out on a limb and guess you don't shoot 1,200 yards too often. A 20" error is a major mistake.

*

 

[Richard of Oz]

Richard.

I make the rules and I enforce them.

You have a choice, there are many other forum sites on the net that will allow crude language.

H*** c***! As you said earlier, Len, take 3 long, deep breaths...
America was founded by Puritans, and puritan it remains.