Rifle Scopes Mil-Dots and First Focal Plane Scopes

[sniper848]

I have been looking over all of the information onthe internet about mildot scopes and first focal plane scopes and I am lost.
The new Nightforce NXS 3.5-15 x 50 F1 and don't really know what I am looking at. Does first focal plane mean that the reticle stays the same size at any magnification, therefore can be used for range estimation at any magnification?
Also what are some of the basic principles of the mildot reticle, does the mildot reticle represent a certain measurement at a certain distance or is it just 1/60 of a minute of angle?

 

[Lowlight]

Re: Mil-Dots and First Focal Plane Scopes

Here a starting point:
Switching to a mil / mil scope

 

[LoneWolfUSMC]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sniper848</div><div class="ubbcode-body">Does first focal plane mean that the reticle stays the same size at any magnification, therefore can be used for range estimation at any magnification?</div></div>

Yes


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sniper848</div><div class="ubbcode-body">Also what are some of the basic principles of the mildot reticle, does the mildot reticle represent a certain measurement at a certain distance or is it just 1/60 of a minute of angle?</div></div>

Research Milliradian

http://en.wikipedia.org/wiki/Radian

Basically the Mil Reticle works on a 1:1000 principal. 1 mil (mRad) is 1" at 1000", 1 meter at 1000 meters, etc. It is NOT metric.

 

[Rob01]

Re: Mil-Dots and First Focal Plane Scopes

The reticle appears to grow and shrink when power is adjusted but it stays subtending correctly to the power level so on any power 1 mil will be 1 mil. It's very nice to have when shooting matches or anything else where any stress is involved. Less thinking.

Good choice on the scope by the way. I have two with the MLR reticle.

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

Actually, a first focal-plane reticle changes size as you change magnification, which is why it can be accurately used at any magnification. That is, no matter what the magnification, the graduations on the reticle will cover the same area of the target.

If you increase the power, the reticle and the target both get bigger. If you decrease the power, the reticle and the target both get smaller.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Also what are some of the basic principles of the mildot reticle, does the mildot reticle represent a certain measurement at a certain distance or is it just 1/60 of a minute of angle?</div></div>

One minute of angle is 1/60th of a degree.

There are 2 times pi radians in a circle, which is 6.283. Since there are 1000 milliradians in one radian, there are 6283 milliradians in a circle.

A good article on mil scopes is here:

http://www.excaliburenterprises.com/scopes/mil-dot.html

 

[sniper848]

Re: Mil-Dots and First Focal Plane Scopes

Well how can I use this for range finding if I know my target size in inches? And is the MLR reticle based off of the USMC mil or the Army mil?

 

[doc76251]

Re: Mil-Dots and First Focal Plane Scopes

FFP scopes are a bit un-nerving for some the first time they use them. The reticle grows and shrinks as the power is dialed on and off which is not "normal". The end result is that the reticle will correctly subtend at any power vs a SFP scope where it only works at one power.

A mil is a measure of angle, no more no less. At 100 yards a mil subtends 3.6", at 1K yards it measures 36". It is angular in nature which allows it to be used for ranging if you have the other two sides of the equation.

The math for inches and yards is as follows

27.778 * (the measurement of the target in inches) / # of mils = range in yards.

Example:

18 inch target that measures 1.3 mils in the scope

27.778 * 18 / 1.3 = 384.6 yards

27.778 comes from dividing 1000 yards by 36 inches.

Cheers,

Doc

Damn I'm slow

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

See the article I linked above.

With respect to rifle scopes, there are no Army mils or Marine Corps mils. There are only mils. See:

The Truth About Mils

And note that scopes with the oval dots originally used by the Marine Corps are no longer manufactured. The Marines are using scopes with round 0.2 mil dots.

 

[Rob01]

Re: Mil-Dots and First Focal Plane Scopes

You get your target size in mils by looking through the scope and breaking down the target size to atleast the closest tenth of a mil. The either use a mildot master or the formula:

target size in inches x 27.78 / target size in mils= range in yards

The MLR reticle is a mil based reticle. It is the same mil used in either the USMC or Army scopes.

 

[doc76251]

Re: Mil-Dots and First Focal Plane Scopes

The difference between the Army Mil and the USMC mil is exactly ZERO. A mil is a mil.

The "dot" is the difference.

The Army uses round dots that are .2 mils in diameter
The USMC uses "footballs" that are .25 mils tall

Cheers,

Doc

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

The Marine Corps now uses the same mildots as the Army.

Hi, Doc!

 

[Rob01]

Re: Mil-Dots and First Focal Plane Scopes

But they use them better

LOL

 

[doc76251]

Re: Mil-Dots and First Focal Plane Scopes

Hi Lindy!

I should quit typing now.

You, Rob, and Frank are going to pull out some voodoo that is going to make me sit in the corner with a gonkulator for the next week trying to find an easier way to do it.

For the OP.

GET A MILDOT MASTER!!!!!

Cheers,

Doc

 

[sniper848]

Re: Mil-Dots and First Focal Plane Scopes

Ok thanks guys, I was just confused on where the 27.778 came from but now I understand.

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

If you want some other ways to do that calculation, see:

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Ranging/

Like Doc said, get a Mildot Master.

http://www.mildotmaster.com

 

[LoneWolfUSMC]

Re: Mil-Dots and First Focal Plane Scopes

Yep, MDMs are the best when it's raining and sloppy and you aren't thinking clearly.

 

[sscoyote]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sniper848</div><div class="ubbcode-body">Ok thanks guys, I was just confused on where the 27.778 came from but now I understand. </div></div>

That's the whole kicker in the equation. Once u understand that concept (what i call the "subtension unit factor"), u will see that the mil-ranging formula is not specific to the milliradian 3.6 IPHY subtension at all, but in fact can be used with any multi-stadia reticle and subtension. That concept is way bigger than the mil-dot reticle itself--

Gots a plex reticle in your arsenal? Measure it, then calculate it's own specific "SU factor" and apply it the same as a mil-dot for rangefinding. This is when it really gets fun...IMO!

 

[HillbillyfromAL]

Re: Mil-Dots and First Focal Plane Scopes

Sniper848: try out this website it'll help you visualize it. And it's good practice for milling when you can't get to a range. Hell of a screen name for asking questions like these, but whatever right.

http://www.shooterready.com/lrsdemohi.html

 

[sniper848]

Re: Mil-Dots and First Focal Plane Scopes

"Hell of a screen name for asking questions like these, but whatever right."
Well I was going to make it HillbillyfromAL, but that was taken! lol

 

[Graham]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body">MDMs are the best when it's raining and sloppy and you aren't thinking clearly.</div></div>I thought that's what spotters are for.

Seriously, lots of good info above on this Thread.

 

[Austan]

Re: Mil-Dots and First Focal Plane Scopes

Tagged for nerding out on math later!!

 

[JL]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: doc76251</div><div class="ubbcode-body">The difference between the Army Mil and the USMC mil is exactly ZERO. A mil is a mil.

The "dot" is the difference.

The Army uses round dots that are .2 mils in diameter
The USMC uses "footballs" that are .25 mils tall

Cheers,

Doc </div></div>

term "mil" can mean 3 different things: angular unit based on 6000, 6283 or 6400 -circle.
All are mils, but not same. Thats why, for example, S&B turret says "mrad" instead of "mil". And thats 6283.

"milliradian", or "mrad",system used in modern western sniper scopes is named "mil" in american spoken language.
Still, term itself is not literal.

P.S. About commerical mildots,
Zeiss uses 0.2mrad or 0.25mrad dots in their standard mildot reticles, S&B 0.24 or 0.2mrad, depending model.
Not sure if USMC new S&B scope is based on S&B std Gen 2 reticle or not, but S&B G2 reticle is with 0.2mrad dots.

 

[HillbillyfromAL]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sniper848</div><div class="ubbcode-body">"Hell of a screen name for asking questions like these, but whatever right."
Well I was going to make it HillbillyfromAL, but that was taken! lol

</div></div>

Good one man, Good luck with getting started. Long Range shooting is like meth, one try and your hooked.

 

[Sam Hail]

Re: Mil-Dots and First Focal Plane Scopes

Good laser and spare batteries = GTG
Trust the technology, dial it up and send it !!!

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">term "mil" can mean 3 different things: angular unit based on 6000, 6283 or 6400 -circle.</div></div>

That's sort of like saying that since some people think the earth is flat, it's OK to refer to it that way.

A radian is a well-defined term of angular measurement.

So is the prefix "mil" or "milli", which means 1/1000th of some measurement. (People whose system of measurement is English sometimes use "mil" to mean 1/1000th of an inch.)

But milliradian can only mean 1/1000th of a radian, a quantity of which there are 6283 in a circle.

If there are 6000 or 6400 of something in a circle, the base unit <span style="font-style: italic">cannot</span> be the radian.

That's why I prefer to use the term milliradian, so there's no doubt what I am referring to.

Sloppiness in units leads to problems of the sort which resulted in a spacecraft smashing into Mars instead of making a soft landing. Those errors are best avoided.

 

[pevrs114]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">term "mil" can mean 3 different things: angular unit based on 6000, 6283 or 6400 -circle.</div></div>

That's sort of like saying that since some people think the earth is flat, it's OK to refer to it that way.

A radian is a well-defined term of angular measurement.

So is the prefix "mil" or "milli", which means 1/1000th of some measurement. (People whose system of measurement is English sometimes use "mil" to mean 1/1000th of an inch.)

But milliradian can only mean 1/1000th of a radian, a quantity of which there are 6283 in a circle.

If there are 6000 or 6400 of something in a circle, the base unit <span style="font-style: italic">cannot</span> be the radian.

That's why I prefer to use the term milliradian, so there's no doubt what I am referring to.

Sloppiness in units leads to problems of the sort which resulted in a spacecraft smashing into Mars instead of making a soft landing. Those errors are best avoided.
</div></div>

The Army uses 6400 mils in field artillery calculations, I was always told it was for simpler math. Any ideas why they use it?

I really take a look back on my time in FA and see how much applies to precision shooting - from projectile weight being taken into calculation, 2-meter subtense bar, etc.

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

It would not be nice of me to suggest that the Army <span style="font-style: italic">needs</span> simple math, so I wont.

 

[popeye089]

Re: Mil-Dots and First Focal Plane Scopes

Deleted point made

 

[sscoyote]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: popeye089</div><div class="ubbcode-body">Yeah get a mildot master but most importantly learn how to do the math, it's field craft learn it..</div></div>

Exactly, knowing the basic math will help with understanding the equations. In fact several years back i realized that the mil-ranging formula defines downrange zeroing as well, in IPHY, MOA or mil-whatever reticle or turret subtension you're using, since a tgt. size is the same sort of dimension as a trajectory.

Here's the most basic formula (inches to yds.)--

tgt. size (") x range of reticle subtension (usually 100 yds.) / reticle subtension (") / quantity of gap tgt. occupies (decimal equivalent) = range (yds.)

10" tgt. occupies 0.5 mil--

10x100/3.6/0.5= 555 yds.

Suppose the bullet drops 55" from zero at that range, how many mils is that using the above formula? Remember a tgt. size is the same type of dimension as a trajectory--

55x100/3.6/x=555
x=2.75

Nice thing about the formula is that if u invert the bottom 2 divisors u still get the same answer.

Suppose u have the Nikon BM 6-18x mil-dot that subtends correctly at 12x. At 18x the dot to dot subtension becomes 2.4 IPHY insead of 3.6. Here's the equations now for a 10" tgt. @ 555 yds.--

10x100/2.4/x=555
x=0.75 "mils"

now 55" of drop is referenced as--

55x100/2.4/x=555
x=4.1 mils. holdover (so aim at the bottom of the 4th dot).

Beauty of the whole system is that in a second focal plane optic the dot subtension maintains the same relative relationship to the dot to dot subtension at any power (.2X in the case of this optic).

 

[sscoyote]

Re: Mil-Dots and First Focal Plane Scopes

Suppose u're using the Burris Ballistic Plex reticle and that 11" back to brisket coyote gaps .75 of the x-hair to 2nd stadia down (4.1 IPHY)--

11x100/4.1/0.75=360 yds.

Suppose u're drop at that range is 12"--

12x100/1"/x=360
x=3.3 IPHY

1st stadia=1.4 IPHY
2nd stadia =4.1
that means there's 2.7 IPHY beween them (4.1-1.4)
3.3=1.9 more than 1.4
now divide 1.9 by 2.7 and the aiming point is 1.7 (subtension units).

 

[Pete E]

Re: Mil-Dots and First Focal Plane Scopes

As far as land navigation (within Nato anyway), everybody uses 6400 mils regardless of whether your a Marine or Army...
Outside Nato, the Russians, Finns and certain other countries use different standards, so the "Mil" is far from being standard.

In scopes, I think most modern ones use the 1/6283 standard, although I think Leupold did produce ones with Mildots derived from 1/6400 version at one stage.

While Lindy give an outline of one origin of the Mil, in truth it is actually the spawn of the devil put on this earth to taunt those Americans who still hang on to their beloved Imperial measurements!

Regards,

Peter

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

The reticle in the original Leupold M3A was based on the 6400 figure. However, that scope adjusted in 1 MOA clicks, and using a reticle based on the 6400 figure won't lead to major errors. All other modern scopes I know of are based on the milliradian, for which, as I have previously noted, there is only one figure.

I really don't care what people use for artillery or land navigation. There can be many "mils", if by that you mean a fraction of 1/1000th of <span style="font-style: italic">something</span>. There is only <span style="font-weight: bold">ONE</span> milliradian.

As for Imperial versus metric measurements, I'll once more cut-and-paste the truth about that:

There are two times Pi radians in a circle, and a milliradian is simply one-thousands of a radian.

One milliradian is an angle which subtends an arc whose length is 1/1000th of the distance from the vertex.

In other words, one milliradian subtends an arc whose length is:

1 yard at 1000 yards.
1 meter at 1000 meters.
1 mile at 1000 miles.
1 league at 1000 leagues.
1 fathom at 1000 fathoms.
1 inch at 1000 inches.
1 foot at 1000 feet.
1 lightyear at 1000 lightyears.
1 attoparsec at 1000 attoparsecs.
3.6 inches at 3600 inches (100 yards).

It has nothing to do with any Imperial or Metric system of linear measure.

I'll keep doing that until everyone gets the point. I'm not in a hurry, and it's in a file.

 

[Pete E]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">It has nothing to do with any Imperial or Metric system of linear measure. </div></div>

Quite true...But doing the math in metric units is so much easier than imperial....

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

I use a PDA and/or a Mildot Master to do the math. Both are equally fast in either system. I can still do longhand multiplication and division, but I see no reason to.

 

[popeye089]

Re: Mil-Dots and First Focal Plane Scopes

forget it

 

[khronoscide]

Re: Mil-Dots and First Focal Plane Scopes

Hmmm, this ought to get interesting.

 

[Autoguns]

Re: Mil-Dots and First Focal Plane Scopes

excellent thread, thanks posting all the intel...JW

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

Electronic technology is certainly vulnerable. A Mildot Master, though, is not electronic. You might lose it, but it's unlikely to break.

I do not advocate relying on technology.

In fact, I wrote a web page on building density altitude dope tables, so one doesn't have to rely on PDAs in the field. It's here:

Making Ballistic Cards Using Density Altitude

And because I don't like to rely on electronic gadgets like the Kestrel for the DA calculation, I wrote another one on how to manually calculate density altitude, if you must:

Manual Calculation of Density Altitude

So, I'm all about knowing how to do without, if necessary.

My attitude, though, is that while a fool will be unable to operate in the absence of technological assistance, an even bigger fool will fail to take advantage of technological assistance when it is available.

I'm all about practicing fundamentals. And there are some you could benefit from learning and practicing, i.e., capitalization, spelling, punctuation, grammar, and using paragraph breaks.

History shows that fights are won by moving, shooting, and communicating. Your communication skills are weak.

This is usually the result of too much time spent on computers and sending text messages on cell phones. Computers and cell phones break. I expect that you would benefit from more time writing by hand with that ultimate low-tech communication device, the pencil.

 

[doc76251]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: popeye089</div><div class="ubbcode-body">For real? those are your words of wisdom? Be lazy and don't verify that you know how to do it on the drop of the dime? Have you ever had to engage a target on a 2 way range or just shoot from the prone on a KD? Don't listen to this guy, make sure you always practice, because like anything the more you do it eventually the better you get. by using the pda all you know about yourself is that you can move your lil fingers fast, some people's fingers are fatter than others LOL But for real always practice all field crafts,i.e. my section always practices RE, yes we have LRFs but we always use our scopes and then verify with the LRFs. Why because tech always break, I.E. Daggers, anyone who actually served their country in a combat MOS knows when land navin it will give out, that's why we make sure all scout snipers KNOW HOW TO READ & USE a MAP. Do some work, practice, become competent, get good, and don't become another one of those lazy fat Americans that all service members are embarrassed to look at when we get off that plane from country
Scouts Out
Snipers Forward </div></div>

You are an idiot.

I dare say you are also unaware of the company that you keep.

I would also be very surprised to find a DD-214 or an Oath of Enlistment associated with your name.

Cheers,

Doc

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: popeye089</div><div class="ubbcode-body">forget it </div></div>

I may forget - but the web never forgets. Thanks, Doc!

 

[BobinNC]

Re: Mil-Dots and First Focal Plane Scopes

Lindy,

Look at Popeye's profile. He lists his occupation as a "Population Control Specialist". So he's a killer, and proud of it. Other than being a moron, he is a "Legend" in his own mind.

Maybe one of Piston Pete's imaginary little friends......Don't waste your time.

Bob

 

[popeye089]

Re: Mil-Dots and First Focal Plane Scopes

Deleted by made

 

[BobinNC]

Re: Mil-Dots and First Focal Plane Scopes

popeye89,

Good post. I think you should stick around for a while. Your post above means you recognize how you appeared to the rest of us. I respect your service, and your specialty.

If you think Americans are lazy and unproud of their miltary now, you should have tried coming home in 1971. Old history I know, but history I will never forget.

I don't know what infantryman goes through. But my imagination is still pretty active. That's why I sailed around in pretty white boats.

I'm sorry I came down on you so hard.

Best of luck,

Bob

USCG, Operation Market-Time, RVN, IV Corp, 1970-1971

 

[Lindy]

Re: Mil-Dots and First Focal Plane Scopes

Don't worry about it, man.

And thanks for serving your country.

Just realize that it's easy to make snap judgements about something you see online, but you often don't know much about the people behind the post, and what they know.

Lots of us got jumped on in early posts. Stick around, learn. This site is a great source of information.