Shooting Exercise II: Mil Dots


PDA






echo3mike
May 18, 2003, 10:44 PM
Our favorite tactical dude has finally won the lottery and bought a big hunk o' land in the middle of nowhere for the Uber-Tactical Shooters Ranch and BBQ Emporium and Factory. He's asked you to sort of set up a security perimeter to guard his secret BBQ sauces and whatever nubile...workers...he has staffing the place.

He's decided to have you in charge of the guard towers...guard stumps really, just 5 feet above the ground. You've identified likely avenues of approach, addressed the lack of electrical fencing and video cameras, made sure all your security and the local police / fire & rescue folks are on the same radio freqs...the whole enchilada. So you go about sighting in to the building's windows just in case. You've studied the plans and noted that the lowest windows have a top that is only 72" from the ground. So you go about milling these windows from this particular post just to kill some time until the laser range finder finds it's way into your hands.


Window #1 is milled at 2.7 mils
Window #2 is milled at 2.5 mils
Window #3 is milled at 2.4 mils.

Exercise II
A) What are the ranges for windows 1-3?

B) If the other guard tower is NE of your position by 760yds and through your scope is 1.3 mils away from the electrical fence, how far away from the fence is the guard post in inches / feet?

C) In one scenario, you've got the (insert target here) travelling directly in front of you going left to right at 4mph on the road 800ds away from your position. Your bullet (FGM 175gr SMK, BC of .496) takes 1.272 seconds to travel 800 yds with an MV of 2600fps. You've also got an 8mph wind from right to left. Whats your
1) Windage
2) Lead in mills and inches

C is totally unrealistic, but try the exercise none the less.

D) If you were shooting at a deer (lets say a 20" kill zone) that you ranged at 1.4 mils, but was really at 1.7 mils, would this be a clean kill or a miss?

S.

MIldot article (http://www.swfa.com/mildot/)

If you enjoyed reading about "Shooting Exercise II: Mil Dots" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
ShaiVong
May 18, 2003, 11:26 PM
A)
741yrds
800yrds
833yrds

B) Confused on B, still trying to understand question, but i'm getting closer.

C)Not sure about windage, but lead by 39.18 mills? 313.4inches?

14mph=246.4in/sec


Whoops! confused Mil with MOA!

1 Mil=3.6" @ 100 yards.

Lead with... err... ummm...:uhoh:

10.88mils?

echo3mike
May 18, 2003, 11:51 PM
Ooops..

try the last bit again....had to go back and edit. Sorry

S.

Art Eatman
May 18, 2003, 11:52 PM
No reference material, here, and I've never used mils.

For C, 1: At 500 yards, I gotta hold Ol' Pet about 20" or so upwind for about 10mph. For 800, with the bullet slowing down even more, I'd hold about three feet. But my usual load starts out around 3,000, not 2,600. :)

I usually hold about three feet per hundred yards for Bambi, but the car's going about half-a-Bambi. The car is moving about 21 ft/sec (30 mph = 44 ft/sec), or about 26-27 feet during the bullet's flight.

Adding the wind and the car, I'd hold about two car lengths in front of the middle of the hood, for starters. If I'm leading a bit much, I'll get the radiator; maybe the carb/FI. A bit too little, and shame on the driver.

Elevation? I'm having to guess for beyond 500. Four feet of holdover, for my rifle at 500. Maybeso 14 or 15 feet above the line of the hood. Three car-heights high.

And ya gotta figure out all that in about one second, 'cause that car, like Bambi, keeps on moving.

Art

echo3mike
May 18, 2003, 11:57 PM
And you too, Art... thought the first target was a little too "personal", and at that speed, it wasn't really a valid target.


Everyone gets a do-over...unlike reality!

S.

ShaiVong
May 19, 2003, 04:49 PM
Art, your inspiring. :D

Art Eatman
May 19, 2003, 05:19 PM
Watch dust. Adjust. :D I'm basing elevation on my 200-yard zero, which means holding two feet high at 400 and four feet at 500. Moving on out, I'm guessing adding three feet, then four feet and then five feet. So that's 16 feet of holdover. A car is roughly five feet high--omitting Corvettes and suchlike--so three car heights above the hood is about as good as a Mark 1 eyeball can do.

Like I say, I'm just guessing, absent any data or experience for 800. Out to 500, whatever's out there, I pretty much own it--and that's based on experience. :)

Hmmm. It's about a thousand yards from my 500-yard bench to the County Road. Vehicles usually go about 30mph. It'd be good practice, neh? :D Could mount a sheet of plywood on a trailer...

The problem now is that I'll probably go to setting posts for target frames out at 600 through 1,000 and see what happens...Danged folks who're always makin' me work!

Art

Frohickey
May 19, 2003, 06:30 PM
Given:
Windows are 72 inches (2 yards) from the ground
Observer is 5 feet above the ground
Window #1 is 2.7mils
Window #2 is 2.5mils
Window #3 is 2.4mils
Guard stump A is 760 yards from Guard stump B.
Guard stump B is 1.3 mils away from fence.

1 mil = 1/1000 radians

A) Calculator in radian mode:
distance = window height / tan(mil reading/1000)

Window#1: distance = 2 yards / tan(0.0027) = 740.739 yards
Window#2: distance = 2 yards / tan(0.0025) = 799.998 yards
Window#3: distance = 2 yards / tan(0.0024) = 833.332 yards

B) Calculator in radian mode:
distance = fence distance / tan(mil reading/1000)

fence distance = 760 yards * tan(0.0013) = 0.988 yards

C) Sorry, professor, I skipped that chapter. :D

D) Sorry, professor, I'm a vegetarian, at least for today. :p

echo3mike
May 20, 2003, 10:58 PM
Question A

Three 72" windows:

Window #1: 2.7 mils
Window #2: 2.5 mils
Window #3: 2.4 mils

Couple of different equations for this...actually three now that Frohickey has posted his answers.

#1: ((target in yards) X 1000) / mil reading= range in yards

#2: ((target size in inches) X 27.77) / mil reading = range in yards

So..

#1) (72" X 27.77) / 2.7 mils = 740 yds
#2) 799.8 yds
#3) 833 yds

Question B

-This is a little more math-involved. Again, Frohickey's method works out well, but I'd have a hard time remembering to switch my calculator back and forth!

-If 1 mil = 3.6" at 100yds, then at 760 yds, 1 mil equals

3.6" X (range divided by 100 = 7.6) = 27.36" / mil @ 760yds.

-If the space is 1.3 mils, then 1.3mils X 27.36" / mil @760yds = 35.568" or 0.988yds.


Question C

-Obviously more than one way to approach this problem. Since it's totally unrealistic to begin with, there's probably a couple of hundred different ways. The school answer for this is if your target is going to be at a known position, you'll adjust for the windage before the target arrives. The 175gr FGM .308 Win has a great deal of data associated with it's military counter-part, the M118LR cartridge. One bit that can help users is a quick wind equation:

(range factor X wind speed) / range constant = full value MOA adjustment.

With the range factor being range / 100, and the constants are
-100 - 500yds : 15
-600 yds : 14
-700 - 800yds: 13
-900yds : 12
-1000yds: 11

so (8 X 4mph) / 13 = 2.462MOA right windage

- The formula used for leads is an extention of one used above.

-4mph = 5.867fps
-the target will travel 7.46ft / 89.554" in the 1.272 seconds it takes the bullet to travel 800yds. (5.867fps X 1.272sec)
-if one mil = (3.6 X 8) = 28.8" , then
-89.554" target travel / 28.8" per mil at 800yds = 3.12 mils lead left.



Question D

The reason question A and D were posed were to give some indication of how easy it is to make an error using mil dots. In question A, a mistake of .3 mils in the reading can cause an error close to 100yds. Even a .1 mil error can cause a miss, depending on the range.

I'll use the FGM.308 175 / M118LR in the example. The M118LR has a danger space, (a distance where the bullet will strike somewhere in the target area regardless of any ranging error), of 62 meters / 67.8yds at 300 meters / 328.1yds, aiming at a 20" target. That means that at 326yds, ( the 1.7 mil reading), , there can only be an error of 67.8 yds, or + / - 33.9yds. Since you adjusted for 396.7 yds, (1.4 mil reading), the bullet would not strike the target.

S.

Sources:
-S.W.F.A. (http://www.swfa.com/mildot)
-Sniper Country (http://www.snipercountry.com/mil-moa.html)
-Sniper's Paradise (http://www.snipersparadise.com/Marksmanship/range_est.htm)
-FMFM-1-3B: U.S.M.C. Manual: Sniping (https://www.doctrine.USMC.mil/htm/doc5.htm)
-FM 23-10; Army Sniping Manual (http://www.adtdl.army.mil/cgi-bin/atdl.dll/fm/23-10/toc.htm)
- Michaelis, D. 2000 The Complete .50 Caliber Sniping Course: Hard Target Interdiction , Paladin Press. Boulder, CO. p203

If you enjoyed reading about "Shooting Exercise II: Mil Dots" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!