Anyone know a "reverse mil-dot formula"

[Fowlpursuit]

Bo doubt I am making thing complicated- my situation is this- I have a benjiman NPXL 1100. Decided to up grade to the utg 3-12x44 scope and GRT III trigger. Scope is here and still waiting on trigger. Small game season opens today. I realize I'm going to have to spend some Time on the range but don't wanna spend any more time then I have to. I already have tradjectory info for 14.3gr round nose pellets. 10-100 yrds. My hope was to figure out wat a 5" target measures in mils from 10-100 yrds and figure out ness nessacary hold over in relation to my already known tradectories using the math formula. Then I could just do a sight in and confirm my calculations at the range allowing me more time in the feild..

[condor22]

 Ok. Maybe this is necessary.  Set 5in target @ each known distance/known drop, take mil reading of 5in target @ each known and document onto your drop chart. The mils measured will change with magnification, so use the exact magnification you zeroed at or even this won't work! As I said I have no math skills. You should do this after the math anyhow to prove the math. 

[Fowlpursuit]

Yes this is precisely what I will end up doing.(I did the same with the provided centerpoint)Was just hoping to make the math work /just a personall accomplishment I guess and something to take up my time while I wait on the trigger to get here as I wanna do my sighting in wit it installed

[condor22]

 Need Chairgun help!

 Can I add parameters of target size and target distance, just to look at the sight picture/reticle, to accurately see exactly where the mil-dots lay on the target. Would the simulation be exactly same as using the real world target's sight picture?

[Bullit]

Bo doubt I am making thing complicated- my situation is this- I have a benjiman NPXL 1100. Decided to up grade to the utg 3-12x44 scope and GRT III trigger. Scope is here and still waiting on trigger. Small game season opens today. I realize I'm going to have to spend some Time on the range but don't wanna spend any more time then I have to. I already have tradjectory info for 14.3gr round nose pellets. 10-100 yrds. My hope was to figure out wat a 5" target measures in mils from 10-100 yrds and figure out ness nessacary hold over in relation to my already known tradectories using the math formula. Then I could just do a sight in and confirm my calculations at the range allowing me more time in the feild..

If you're still having problems, feel free to contact me via P.M. here on the GTA.  I'll help.

[kristoff1313]

Fowlpursuit, if you go to leapers site for that product download the mil dot PDF they have giving size and mill readings..
however with variable power scopes like 3-12 and having the mil set standard at 10x power you will never be 100% spot on without a stop in place at exactly 10x. With mil dot reticle and MOA turrets a mildot master may be helpful as well. (SWFA has them I think)

Condor22 also pointed out using a known target size at different yards/meters to get the readings on different magnifications (KISS).  If this is a second focal plane reticle be sure the POI stays the same at each distance. Some scopes don't hold it changing magnification if they are SFP in stead of FFP.

Hope this is helpful information and Happy Hunting!

[NHGuide]

http://www.mil-dot.com/media/1027/the_derivation_of_the_range_estimation_equations.pdf

[sscoyote]

I just joined here, and don't know if I should resurrect this thread, but optics applications for long-range shooting and rangefinding is one of my passions. My system for reticle-rangefinding in the field is like this (hypothetical measurements)--

mils-range--

3.0-75
2.5-100
etc.

this way it can be easily referenced in the field when placed in a Butler Creek scope cap cover.

Now when it comes to subtension (reticle) systems for rangefinding (not just mil-dot) the math is as follows (inches to yards)--

tgt. size (") x range of reticle subtension measurement (yds.) / reticle subtension (") / "mil reading" (decimal equivalent) = range (yds.)

looks complicated but very easy to apply, so for your 4" tgt size using the milliradian subtension here's the 1st, say 50-yd. calc--

4 x 100 / 3.6 / X = 50
X=2.2 mils
so your 1st entry is--

2.2-50

now it should be easily seen that 4 x 100/3.6 =111.1 (what I refer to as the tgt/subtension factor), so now the calcs become much faster--

111.1/X=60

1.9=60 (2nd entry)

etc. to as far as the reticle allows you to go efficiently

[sscoyote]

Now, here's another interesting (and very useful) thing to know about reticles in 2nd focal plane scopes--reticle subtension is ~inversely proportional to magnification. That means that if the subtension between like areas between dots (center to center, like edge to like edge), is 3.6" @ 100 yds. @ 10X, then at 12X it'll be 10/12 = X/3.6, X=3.0" @ 100 yds.

Now crank the scope to the optic's highest power (the reticle subtension "stop" as Kristoff mentions above), and you should be at 3.0 " @ 100 yds.

Now use the same formula above and replace the 3.6" subtension variable in the equation with 3.0" and recalc everything. Now you have a more accurate and more precise system of reticle rangefinding.

Yes...it's true that magnification is often slightly different than what's marked on the power ring, but everyone I've ever checked is as calculated.

In my experience 2 very important concepts that should be understood is--

1) The "mil-ranging" formula defines rangefinding (as well as downrange zeroing) with any multi-stadia reticle and tgt. turret.
2) Reticle subtension is ~inversely proportional to magnification in 2nd FP optics.

[Supaflee]

Many hours ago , someone suggested " Use Chairgun "
 What a wonderful bit of advice that was .
 I have a Ballistics chart for all my Airguns , all derived from Chairgun. Its a cool program to play with and the more familiar you use it the more information you will get from it .
 Dont try to re-invent the wheel ,
 Dare to go There !!!
 Supaflee

[Scotchmo]

Now, here's another interesting (and very useful) thing to know about reticles in 2nd focal plane scopes--reticle subtension is ~inversely proportional to magnification. That means that if the subtension between like areas between dots (center to center, like edge to like edge), is 3.6" @ 100 yds. @ 10X, then at 12X it'll be 10/12 = X/3.6, X=3.0" @ 100 yds.

Now crank the scope to the optic's highest power (the reticle subtension "stop" as Kristoff mentions above), and you should be at 3.0 " @ 100 yds.

Now use the same formula above and replace the 3.6" subtension variable in the equation with 3.0" and recalc everything. Now you have a more accurate and more precise system of reticle rangefinding.

Yes...it's true that magnification is often slightly different than what's marked on the power ring, but everyone I've ever checked is as calculated.

In my experience 2 very important concepts that should be understood is--

1) The "mil-ranging" formula defines rangefinding (as well as downrange zeroing) with any multi-stadia reticle and tgt. turret.
2) Reticle subtension is ~inversely proportional to magnification in 2nd FP optics.

Take your 3.0" subtension one step further. Airgun distances are relatively close. If you work in feet rather than yards, it become 1" subtensions. The math then become easy enough to do in your head (I still use charts to speed things up).

At SFP 12X:
A 1" target, spanning 1 dot space, is 100' away.
A 1" target, spanning 2 dot spaces, is 50' away.
etc.

[sscoyote]

I see it Scott...it all comes down to units--

inches x yds./inches = yds.

or

inches x ft./inches = ft.

Have often been fascinated by the math, and have seen some impressive things happen by using and manipulating it.

[Bullit]

If you look at feet conversion and inch subtentions,  you can "trim everything down" to airgun users. 
12/10x....9/10x....6/10x etc is really easy with a calculator. 
Just use 10x as your basis, and remember that at 10x is the MILDOT standard:
The MILDOT 10x standard Center to Center from the Crosshair zero is:
 Center to Center @ 100yds, 1Midot= 3.6"    @50 yds, 1Mildot=1.8"    @25yds, 1Mildot=7/8"

[Scotchmo]

If you look at feet conversion and inch subtentions,  you can "trim everything down" to airgun users. 
12/10x....9/10x....6/10x etc is really easy with a calculator. 
Just use 10x as your basis, and remember that at 10x is the MILDOT standard:
The MILDOT 10x standard Center to Center from the Crosshair zero is:
 Center to Center @ 100yds, 1Midot= 3.6"    @50 yds, 1Mildot=1.8"    @25yds, 1Mildot=7/8"

A standard mil-dot (usualy at 10x) is a milliradian which is 1/1000 of a radian. So:

At 1000 yards, each dot spans 1 yard.
At 1000 inches, each dot spans 1 inch.
At 1000 meters, each dot spans 1 meter.

That is the basis for it all. Don't mix units and there is NO conversion factor. Or, mix the units and magnification any way that you want, but just use the appropriate scale factors.

[sscoyote]

I've seen some amazing things accomplished with the "mil-ranging formula" in it's most basic form. Understanding the formula completely allows it to be applied for more than just the mil-dot reticle. It can be used with any 2 points at one distance relative to any 2 points at any other distance. I've used it with iron sites, and even archery sight pins for rangefinding and it also defines downrange zeroing as well, since a bullet or pellet drop at any distance is the same type of dimension as a target size.

The 2 best things about the mil-ranging formula is that it's easily memorized, and it's adaptable to more than one application.

[rash_powder]

If,

Range (yards) = {size (yards) * 1000}/mils

and size = 4 inches = .111 yards,

then

Range (yards) = {.111 * 1000}/mils = 111/mils

and

***range/111 = mils***

It is very easy to set this up in a spread sheet and have it crank out the range, size, mils, whatever you like for hundreds of values.  For things like this Xcel or whatever Libre office or Open office calls it is your friend.