# optic ranging

Discussion in 'Long Range Hunting & Shooting' started by load, May 23, 2012.

Messages:
366
Joined:
Jan 18, 2010
While shooting lines with a theodolite the other day I started wondering several things.
One thing I was thinking about was.. if stadia is simply 1 in 100 than what ratio is a mil-dot. I have used the "size of the target in yards x 1000 / mil reading" and "size of the target in inches / mil reading x 27.776" but never really thought about ratios.
I started playing with the numbers.... 1 mil is roughly 3.6" in 100 yrds or 3.6" in 300 feet or 1 inch in 83.333 feet or 1 inch in 1000 inches.
If I follow 1 inch in 83.333 feet I could also figure the following..." target in inches / mil reading x 83.333 / 3 = range in yards" it would also make sence that " size of the target / mil reading x 1000 / 36 = range in yards"gun)

If one minute of angle is 1.04" in 100 yrds than it follows that 1 minute is also 1.04 in 300 feet or 1 in 3461.53 or 1 inch in 96.15 yards so it would also follow that the size of the target in inches / minutes x 96.15 = yards to target" or " size of target in inches / 1.04 / minutes x 100 = range in yrds"gun)

This also gave me the idea to see what ratios my variable scope could equate to and if I could reliably use them to range. I decided to use my Millett lrs-1. This scope "mils" at 12.5 x and is 1/2 mil at 25 x. I divided 1 by 12.5 and came out with .08. To quick check I multiplied .08 by 25 and came up with 2. so it followed that if I divided the mil reading by (.08 x power setting ) and substituted that number for mil reading than I could range at power level. Than set up a tape measure at 100 yrds to check my theory. and IT WORKED!!

so it follows that "size of the target in inches /( mil reading / ( (1/mil power) x power))x83.333 / 3 = range to target in yards"gun)

2. ### sscoyoteWell-Known Member

Messages:
1,255
Joined:
Feb 26, 2003
Pretty good Load--I also like to play with the math behind reticle rangefinding. As it turns out the equation actually defines the reticle and turret reference for downrange zeoing as well. I apply the mil-ranging formula with any reticle subtension, from simple plex to Ballistic Plex and anything in between. Here's the formula i use--

tgt. size [inches] x range of reticle subtension measurement [yds.] / reticle subtension [inches] / "mil-reading" = range [yds.]

It also helps to know that reticle subtension is inversely proportional to magnification in 2nd focal plane scopes as u noted above.

Here's a couple youtubes i did on these concepts since they're way bigger than simply mil-dot ranging and downrange zeroing--

[ame=http://www.youtube.com/watch?v=ozEhoNaRi2s]Pt. 2) More Reticle-Rangefinding Math Including 2nd Focal Plane Reticles. - YouTube[/ame]

Messages:
366
Joined:
Jan 18, 2010
sweet!!gun)
so on the second video mil power/desired power x 3.6= new "milling"

4. ### sscoyoteWell-Known Member

Messages:
1,255
Joined:
Feb 26, 2003
Yeah, that's it.

Awhile back some guy was wondering how a circle dot reticle could be used for rangefinding a target that was really too small for the unit of subtension of the reticle [from center dot to edge of circle--1/2 the circle's diameter actually]. The problem was that the target was too small for that subtension. Somehow i figured out how to use the target as the subtension and the reticle as the tgt. But i can't remember how i did it--i'll have to look at the math some to see how i stumbled onto the solution.

5. ### rsbibleMember

Messages:
16
Joined:
Apr 27, 2012
Great info and thanks for the Youtube videos. I think I'll have to watch them a couple of times