MIL vs MOA

[cmshoot]

This a Trijicon Mil reticle, what are the graduations in? Basically the 5 represents how many inches, centimeters or ???? Just new to all of this.

The numbers represent mils.

 

[cmshoot]

The formula I always remember for mils is:

Size of target (units)/size of target (mils) x 1000 = distance to target(units). Just keep the same units and you are good. Size of object in yards = range in yards. Height or width each work.

It is important to remember that unless you have a first focal plane optic it only works at one magnification. For those that may not know, first focal plane means the reticle gets bigger if you turn up the scope magnification. If the reticle stays the same a regardless of scope power setting them you have a second focal plane scope.

Most second plane scope manufacturers I've dealt with say the reticle "works" at the highest power setting; however, I have found this is not always exactly accurate. I always double check with a known target at a known range to see which power setting matches.

And yes, it could just be MY eyes that are off; but they're the eyes I'll be using!

Actually, you can also range at any power with an SFP scope; it adds 1 step to your math equation. Not as quick n' easy as an FFP, and the FFP also has the advantages of holdoffs and leads at any power, but has the downside of a reticle that will often change size in a manner that is counterproductive.

To range at any power with the SFP, if you take the power you want to range with, and divide it by the power you're supposed to range with, you'll end up with a number. Take that number and multiply it by the MOA/mil number you got when ranging.

Example:

You have a 6x-24x scope that is set to range at 14x from the factory, and you want to range on 24x, here's what ya do:

Range as you normally would. Take the mil reading and divide it by 1.71. Then factor the new mil reading into the standard formula.

1.71 is obtained by dividing 24x by 14x: 24 / 14 = 1.71. You divide the power you want to range with by the pre-set ranging power.

You can use this method for any power on your scope, i.e., if you want to range on 20x: 20 / 14 = 1.43

So, you have a known target size of 20". You range and get a reading of 2.225 mils. Your formula when ranging at 14x would be:

(Size target in inches X 27.778) / mils = distance in yards

(20 x 27.778) / 2.225 = 250 yards

If you were ranging at 24x, take your mil reading of 2.225 and divide by 1.71:
2.225 / 1.71 = 1.3 is your new mil reading.

The formula would be: (20 x 27.778) / 1.3 = 427yds

Easy thing to do is to go ahead and figure out the adjustments ahead of time and write 'em down.

 

[mtdawg169]

All this math has my head spinning.

cmshoot I have a Vortex Viper PST 4-16x SFP in mil/mil. It's mounted on my 5.56 18" SPR. Currently, with a 100 yd zero my turret sits at the "3" mark on the elevation turret. That means that I've got 2 full rotations of adjustment left in the turret (10 mils). Does that sound normal?

I've heard that dialing the turrets to their max can put stress on the scope and shouldn't be done. Currently, my 600 yd dope calls for 4.5 mils. That's the farthest that I've been able to shoot that gun. According to Strelock, 800 yds would call for 7.9 mils, 900 is 10.1 mils and 1,000 would be 12.7 mils. Basically, I can only dial for range out to about 875 - 900 yards if the calculations are correct.

Would a 20 MOA scope base give me additional adjustment range? Or do you just hold over once you've maxed out the adjustment? Is it OK to dial up until the turret stops?

Or is 800-900 about the realistic limit for 5.56?

 

[REDX]

20 moa will give you more adjustment

 

[mtdawg169]

20 moa will give you more adjustment

In my case, with 5.56 loads, would it matter?

 

[REDX]

no

 

[cmshoot]

While a tapered base provides more elevation travel via adding additional bias to the mechanical adjustment system in the scope, the other benefit that it provides is often overlooked.

It keeps the majority of your adjustment range in the "Clean" optical portion of the viewable glass. The illustration shows the viewable portion broken down into thirds. The top and bottom third are considered areas to have more visible optical trash in the field of view (FOV) while the center third is considered to be much more clean. By using a tapered base, it allows you to zero at the lower portion of the "Clean" optical portion and allowing you to maintain the majority of your adjustment travel in that "Clean" portion of your FOV.

The drawing also illustrates the math involved in determining your ability to zero at 100 yards. When you add the tapered base, it allows the erector tube to look lower than it could mechanically; hence increasing your elevation range while providing adjustment travel in your optimal zone. The erector tube in a scope looks down to move POI up and it looks up to move POI down as shown in the drawing.

The word trash is used to describe the characteristics of lesser optical quality; Chromatic and Spherical aberrations, curvature of field, fish eye effect, etc.
Even the best optics exhibit this trash when optics are viewed around the edges/curves of the glass. Some wayyyyy more noticeable than others.

 

[Wallace's]

View attachment 1107443

While a tapered base provides more elevation travel via adding additional bias to the mechanical adjustment system in the scope, the other benefit that it provides is often overlooked.

It keeps the majority of your adjustment range in the "Clean" optical portion of the viewable glass. The illustration shows the viewable portion broken down into thirds. The top and bottom third are considered areas to have more visible optical trash in the field of view (FOV) while the center third is considered to be much more clean. By using a tapered base, it allows you to zero at the lower portion of the "Clean" optical portion and allowing you to maintain the majority of your adjustment travel in that "Clean" portion of your FOV.

The drawing also illustrates the math involved in determining your ability to zero at 100 yards. When you add the tapered base, it allows the erector tube to look lower than it could mechanically; hence increasing your elevation range while providing adjustment travel in your optimal zone. The erector tube in a scope looks down to move POI up and it looks up to move POI down as shown in the drawing.

The word trash is used to describe the characteristics of lesser optical quality; Chromatic and Spherical aberrations, curvature of field, fish eye effect, etc.
Even the best optics exhibit this trash when optics are viewed around the edges/curves of the glass. Some wayyyyy more noticeable than others.

I still need to email you about the 5-6 slides I never asked for from your last optics class. Good stuff. Going to try and make your next one as well.

 

[freedom]

Subbed. Good info.

 

[mtdawg169]

So I've been doing a little digging this evening. It looks like a 20 MOA base would give 5.7 Mils of additional adjust. That's a gain of a little more than one full rotation on the turret. Now I have some pondering to do, based on cmshoot 's post regarding optical clarity within the adjustment range.