Question about mil dots and ranging

[bombadillo]

So I was trying to explain to a guy that a mil-dot doesn't work the same for a 5.56 bullet as a 7.62x51 as a .300 win-mag. He thinks that the dots are the same for all bullets at all distances and I was having a hard time getting my point across about bullet dynamics of trajectory and he was having none of it. Is there a simple website or anything that I can just email him to explain this stuff a little better. He wants to put an NCstar junk scope on an AR10 calibrated for bullet drop of .223 and I don't know how to explain it any better than I have. I usually just drop it, but I want to at least explain before he wastes any money on the dots. He just said, "it doesn't matter, just do the math and you're good"

Anything would help!

[10fcp]

http://files.thetallengineer.com/RangeEstimation_Rev1.pdf

This site explains it real well. To put it simple a 308 and a 223 have different trajectories and those pre set scopes are designed for a specific caliber and not all of them.

[Vtec44]

I'd just let him do the work and verify it. If he thinks he's right, just let him prove it. You both should go to the range and test out his calculation. After that, then you can show him the right way to sight in his AR10.

[Fjold]

Mildots are a unit of measure, not trajectory compensation. The cartridge that you shoot has nothing to do with Mildots.

[Sheldon]

Mildots are a unit of measure, not trajectory compensation. The cartridge that you shoot has nothing to do with Mildots.

Yeah, what he said. You're mixing up a bullet drop compensator (BCD) with mildots. The BCD is calibrated for a specific trajectory, whereas mildots aren't.

[Timberwolf]

Yeah, what he said. You're mixing up a bullet drop compensator (BCD) with mildots. The BCD is calibrated for a specific trajectory, whereas mildots aren't.

Bingo - 1 mil = 3.6 MOA no matter whether its mounted on a 223, 308, 300WM, 338LM or 50BMG

[bombadillo]

I'd just let him do the work and verify it. If he thinks he's right, just let him prove it. You both should go to the range and test out his calculation. After that, then you can show him the right way to sight in his AR10.

This is what I thought initially. I know what he's saying, but I'm trying to save a few bucks and have him not get something with a bullet drop compensator because he's looking at all ar15 stuff and I'm trying not to be a jerk.

Yeah, what he said. You're mixing up a bullet drop compensator (BCD) with mildots. The BCD is calibrated for a specific trajectory, whereas mildots aren't.

You're exactly right, I was trying to say BDC, not necessarily a Mil dot. Thats where he's going wrong is trying to get a BDC for .223 and not a .308 and he was arguing to the bank on it.

[L8Apex619]

You're exactly right, I was trying to say BDC, not necessarily a Mil dot. Thats where he's going wrong is trying to get a BDC for .223 and not a .308 and he was arguing to the bank on it.

Well, as in the OP you referenced "mil-dot" by name, maybe he intended to get a mil-dot (instead of a BDC) all along and knew exactly what he was talking about after all.

[bombadillo]

Sorry, threw the terminology out there wrong in a hurry. What are ya gonna do??

[five.five-six]

one of my mildot scopes has various cams that can be exchanged depending on what you are shooting...556 .308, and .300wm

[Fjold]

one of my mildot scopes has various cams that can be exchanged depending on what you are shooting...556 .308, and .300wm

You have a BDC scope not a Mildot one. Mildots are a fixed unit of measure there are no replaceable cams, etc. to change the distance between the dots.

[five.five-six]

no, it's milldot, with a fixed front focal plane. the retical is in milliradian, but the scope clicks in fractions of a minute. the elevation turret has distances hashed into it. once you 0 it at 100, you can dial it out to 1k fairly quickly and it is fairly accurate

[L8Apex619]

one of my mildot scopes has various cams that can be exchanged depending on what you are shooting...556 .308, and .300wm

This is interesting to me, as mil dots simply allow you to estimate range, and are caliber independent. A milliradian is always going to equal 3.6 MOA.

That's just geometry*. Nothing more, nothing less...

In other words, by its very definition, a mil dot scope will not - cannot - vary from caliber to caliber.

Could you post the make/model of the scope?



*Actually, it's military geometry... A true geometric radian is always going to be equal +/- 57.3 degrees. Similarly, a milliradian will always be equal to +/- 3.44 MOA. However, a military compass has 6400 milliradians in a circle as opposed to 6283.2 (=2*pi). This equates to 3.6 MOA per milliradian (instead of +/-3.44).


.

[five.five-six]

it is not military geometry, it is one portion of geometry that the military adopted

http://swfa.com/Leupold-35-10x40-Mark-4-LRT-30mm-Riflescope-P3320.aspx

anyway, the elevation turret has hash-marks for different distances biased on the cartage you select... just put the correct "cam" for the rifle it is mounted

[L8Apex619]

it is not military geometry, it is one portion of geometry that the military adopted

http://swfa.com/Leupold-35-10x40-Mark-4-LRT-30mm-Riflescope-P3320.aspx

anyway, the elevation turret has hash-marks for different distances biased on the cartage you select... just put the correct "cam" for the rifle it is mounted

A milliradian is a geometric measurement. A "mil dot" equals one milliradian of measurement, and is thus a geometrical unit of measurement.

There are 2pi radians in a circle. 2*pi = 6.2832. Therefore, there are 6,283.2 milliradians in a circle. This equates to 3.44 MOA per milliradian, or distance between two mil dots.

However, the military decided to change this measurement in the context of a military compass to reflect 6,400 milliradians in a circle. This resulted in 1 milliradian equaling 3.6 MOA instead of 3.44 MOA.

So, the military didn't simply "adopt" the geometry. They in fact changed it. Thus the term "military geometry," because in actual geometry, there are only 6,283.2 mil rads in a circle, not 6,400.

I hope that is clear.

Now, regarding your scope (nice scope, BTW), from what you described (hash marks instead of dots), it sounds like you have the tactical milling reticle, which is different from a mil dot reticle, and according to Leupold, unlike the mil dot reticle, is caliber-dependent.

By contrast, a mil dot reticle is not caliber dependent.



ETA - I just noticed you were referencing your scope's dials, and not the reticle itself. From what I can gather, Leupold offers BDC dials on their scopes. Like I said, nice scope!

However, this does not, in any way, change the fact a mil dot is a mil dot is a mil dot - a unit of measurement that does not vary from caliber to caliber... 300 meters is 300 meters regardless whether you're shooting a .308 or a 300 WM. And 3.6 MOA at 300 meters is always going to be 10.8 inches, whether you're shooting a .223 or a .375 H&H. The distance between two mil dots is always going to equal 3.6 MOA, whether or not a scope has BDC dials.