# MilDot Calculations and zoom

Discussion in 'Long Range Scopes and Other Optics' started by peterb, Jun 5, 2009.

1. ### peterbActive Member

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Jul 17, 2008
I have been using a MilDot reticle with a reasonable degree of success, but due to my eyesight not being as good as it could, have tried an alternaive method.
On my scope, the MilDot is accurate at 10 power only. At 500 yards, 1 Mil measures 18"(as we all know). If I increase the zoom power to 19 (10 - 40 x 50mm), then that 18"on my target covers 2Mils. So, as the range increases, if I use that zoom increase with the appropriate calculations, will I still find the measurement of range just as accurate as if left at 10 power?
My reason for asking is that over 500 yards, smaller animals such as Australian foxes are a bit hard to see well enough to accurately gauge the range. Zooming in will make a big difference.

Last edited: Jun 5, 2009
2. ### fr3db3arWell-Known Member

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Yes....if you use your power is to 10x as new mil measurement is to one mil.

IE...if you're using 20x....you cut your distance measure in half.

This is just all learned from using the mildot in "Long Range Shooting Simulator"

3. ### peterbActive Member

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Thanks.
I was "shooting in" a scope at 100 yd increments out to 1000yds, but was having problems seeing the target centre (home made) at the further ranges, so drew a couple of lines on the side of the target 18" apart and then started fiddling with the zoom. It appeared to work reasonably well when matched to the rangefinder, but as if often said : " If it's too good to be true, it generally is ", so I thought I would ask the question.

4. ### fr3db3arWell-Known Member

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I'm still working on it......anything past 800 yards gets iffy for me.

5. ### theodoreWell-Known Member

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Feb 9, 2009
This wouldn't be a problem if the reticle was in the first focal plane.

I'm currently trying out the horus vision scope with its awesome reticle and front focal plane.

6. ### cdoubleuMember

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Jun 1, 2009
The Horus Reticle system or any First Focal Plane (FFP) is awesome for ranging if you are doing the calculations, even better for quick corrected shots. I've got one of there H37 reticles and the only thing that works against this system IMO is that the thickness of the hash marks increases proportionally with magnification (they are super-fine lines to start with, so it's really not much of an issue) which is the oposite of a second focal plane scope that is common. With the FFP the hash mark increaments don't change the measurement no matter what the magnification. I think what peter was noting was that he doesn't need to make much of a calulation because the proportional change in magnification is equal to that of the range. It's a smart solution for his problem. If you are willing to make some very simple calculations, I have to back theodore with the Horus system. It's simply phenomenal.

7. ### LouBoydWell-Known Member

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PeterB:
Since your scope is 10-40x and reads in mils (milliradians) at 10x it will read exactly in inches per dot spacing at 100 yards if you set it at 36x magnification. You then simply estimate the number of inches the portion of the object you're looking at is high or wide between any two adjacent dots. That number is the distance to the object in hundreds of yards. That works well for people used to thinking in inches and yards. For people who are used to the metric system Mils are easier.

The limit on accuracy is only how accurately you can judge the physical size of the objects. That's why I use laser rangefinders instead.

8. ### peterbActive Member

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Thanks guys, I am not at all familiar with the Horus system, but will soon rectify that.
I must admit Lou that it had not occurred to me to shift the zoom to 36. That is too easy.
I have done quite a lot of reading and practice on the MilDot and enjoy the challenge of working with it. The style of shooting I now prefer (the quiet satisfaction of achievement) is to set up in the bush and shoot kangaroos off crops. Occasionally a fox turns up as well. So, my shots have to be right first time, and in saying that, usually have all the time in the world for mental calculations.
I guess the enjoyment is more about the process than anything else.
However, both your comments have encouraged me to dig a little further and push the old 308 out longer.
Around here though, it is hard to find targets out to or over 1000yards because of the terrain.
By the way, I prefer to work in imperial even though Oz is metric. I can see an acre, but I am hanged if I can see a hectare !

Cheers,

Pete.

9. ### gperry99New Member

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May 24, 2009
A brief review of the basics is in order. First the spacing between reference bars of a reticle located in the 1st focal plane do not change with operating power of the scope but the lines get darker and thicker as you decrease power from the calibration power. Secondly, for reticles in the 2nd focal plane the spacing between the reference bars changes by the ratio of the calibration power divided by the operating power. The lower the power the greater the distance between the reference bars. These principles apply to all ranging reticles (MOA, mil radian, inches per 100 yards, and cm per 100 meters). By playing with this ratio it is possible to change 2 MOA spacing to 1 mil radian spacing for example.

If you are using a BDC elevation adjustment dial you need to remember that it is a cam that causes the elevation to change in accordance with the bullet trajectory curve at some standard conditions. The better vendors clearly identify these conditions. If you are shooting at "non standard" conditions you will need to manually dial in a bias value to compensate for the change in base conditions. The current version of Exbal (PC version 9.6) has a feature that will generate BDC quick reference cards that give you the information needed to use either a BDC elevation adjustment, a BDC reticle, or both under varying atmospheric conditions and incline angles.

10. ### peterbActive Member

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You are going to love this !

I was actually doing quite well keeping up with you guys until gperry99 turned up. Now it has gone a little pear shaped on me.
I am familiar with the 1st focal and 2nd focal plane, but after that things get a bit cloudy.
I dont use a BDC, or any computer software to work distances and bullet drop etc, but physically go out and shoot (in the back paddock !).
Spose it is nice to have that sort of opportunity.
I must say though. By actually physically ranging a scope (dial up method) you really do start to understand a hell of a lot about bullet behaviour and shooting techniques. This exercise in itself has enabled me to be quite confident on a target at say 700 yards, that I would have been really dubious about 12 months ago. I am also 3/4's of the way through building my Flash Card which is proving invaluable.
Anyway, you guys have collectively given me a lot to work on and I thank you for that.
It is great to actually talk to someone who actually uses this method of ranging. No one around here uses the MilDot and most have not heard of it.
Incidentally, nobody around here seems to shoot long range at all ; most go spotlighting (max out at 250 yards), but I am finding that other methods draw my enthusiasm much more these days. (Probably something to do with not needing the adrenalin rushes I used to !)

11. ### silvertip-coWell-Known Member

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All this calculus gives me a headache, but I have a 4-16x44 mildot andneed to learn how to range at long range with it. Ouch. I need to read some of the mildot posts ten times and make notes.

12. ### gperry99New Member

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Someone asked what do you need other than practice to make you an effective shooter. Excellent question.

Here is a real life example of why you may want the best tools you can get your hands on.

Early in 2009, four Taliban militants in Afghanistan near the Pakistan border beheaded some local citizens. A team of Special Operations and Navy Seal snipers was assembled to locate and make the four militants cease and desist. After several days of scouring the mountains the militants were located. An observation post was quickly set up. It was located 2100 meters (1.3 miles) from the militants at an altitude of approximately 10,000 feet, and bone chilling wind. The team spotter had the best laser rangefinder money can buy, a Pocket PC with their favorite ballistic program, an electronic wind gauge plus other supporting tools. In a few seconds the shooter was in position with a solid bipod rest. On command he squeezed off a single round and 3.5 seconds later there was one less militant. Air support was called in to flush the remaining three militants out of their hiding spot and two of those were killed by cannon and machine gun fire from the aircraft. The last one was shot by the sniper while trying to climb further up the mountain to escape the area. The important facts are the shooter had no time to practice and his first shot had to be perfect. Incidently there was more adjustment required for the wind than for the bullet drop at 2100 meters.

This team became proficient by practicing making the first shot perfect every time under fresh conditions. They used every tool they could get their hands on to help them accomplish that. They practiced shooting from under bales of hay, from rocking boats at sea, from the top or rocks, and from lots of other uncomfortable postitions.

13. ### peterbActive Member

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Well GP, that is one interesting little story. Don't spose you were involved by any chance ?
Secondly, I am trying to ascertain whether you are trying to make me feel better, or more inadequate. As I mentioned before (somewhere), I don't use portable electronic equipment at all. I must seem really old school to you chaps, but that's the way I am. Also, I could be classed as frugal.
I do try and make 'one shot, one kill ' as often as I can, whether it be real live animal targets or just a target set up.
I was absolutely amazed to read somewhere in this site - of guys who shoot at looong range and quite often have a practice shot to test wind etc. Unfortunately, I don't have those luxuries. Generally, if you do happen to miss, you are dead lucky to get a second shot of any sort. Occasionally, I manage to position myself so the animals I shoot can't tell where the shot is coming from. In that couple of seconds of confusion, I occasionally get another target to shoot. The rifle I use is a 308 range rifle. Single shot, stainless barrel, custom wood stock and Lee Enfield 303 action, so you can see why I am so particular about the one shot - it has to count !
Anyway, I am still going to work on my MilDots with the zoom then verify with a vehicle speedometer. Pretty rough I know, but it works for me.
Cheers,
Pete.

14. ### sscoyoteWell-Known Member

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Pete, all 2nd focal plane reticles that have more than one stadia point in them will change subtension (measurement) inversely with magnification (assuming the power ring is calibrated properly). Best to go out and measure it really to fine adjust it for any subtension u may want. If u go here and study you can see how the mil-ranging formula can be used with any reticle subtension--not just 3.6 inch per hundred yds. www.ottllc.com/specialtypistols/sp20.pdf --Item C) Reticle Rangefinding

I have a 6-18x Nikon Buckmasters mil-dot on a 17 Fireball XP-100 handgun that i use for prairie dogs. That optic is cald. for 12x. At 18 the mil-dot subtension is 66% smaller at 2.4 IPHY (12x is 66% of 18x). Dot itself is now a 1/2" dot instead of 3/4". I use this system for windage and turrets for elevation.