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Old November 20, 2011, 08:23 AM   #1
hodaka
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Binocular range finding grid question

I have my grandfather's M6 WWII binoculars. They were made by Universal Camera in 1942. Does anyone know how to use the range finding grid that is found in the right lense? There are two parallel bars in the center and a vertical and horizontal axis with numbers. Google has helped me locate a number of similar binoculars, but no help with the range finding grid. Thanks.
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Old November 21, 2011, 11:55 AM   #2
Major Dave (retired)
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I don't remember all the details, but...

when I was a young Field Arty LT, 1964, I was given a pair of bino's, 7X50, IIRC, to use to train to adjust arty fires from Observation Posts near the impact zone at Ft. Lewis, WA.

Although the bino's I was issued were not M6's, the principle of the reticle design was the same - designed to allow measurement of vertical and horizontal deviation from the target to the artillery rounds fired in the "adjustment phase" of target engagement with artillery.

More specifically - the horizontal line in the reticle was marked at 10 mil intervals, both left and right of center. So the observer centered the reticle on the target, then noted how many mils left or right the incoming rounds (usually 2 arty rounds fired simultaneouly by adjacent cannons at the firing site) missed the target.

After observing the left/right deviation in mils, the observer multiplied that deviation by the distance (in thousands) from observer to target (called "the T factor), and notified the Fire Direction Center, by radio, of the adjustment needed to bring the adjusting rounds on line with the target.

We used the 2 short parallel lines in the center of the reticle just to keep the target in the center of the field of view.

As for the vertical reticle to the far right side of the field of view, it was not used for field arty purposes. I inquired about its use, and was told that, "It has something to do with adjusting machinegun fires".

About seven years later, as a Captain, I researched "controlled fires" machine gun "barrages", as a WW I tactic, and a very deadly tactic it was, but I never found the connection between the vertical bino reticle and the tactic.

Ask a Fort Benning GA "Infantry Board" alumnus.
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Old November 21, 2011, 05:33 PM   #3
hodaka
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Thanks Dave. That is helpful. I was thinking the parallel bars could be used to estimate range, once I get them calibrated. I will take them to the range next time and see how much height they measure at 100 yds. The numbers on the vertical scale are confusing since they show a "5" at the top then a "20" at the bottom. I was trying to make degrees of angle out of it. Since I have little need to control fire my machine guns I will simply ignore the vertical scale.

Thanks again. BTW - these are surprisingly good binoculars although they have had heavy use.
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Old November 21, 2011, 06:35 PM   #4
kraigwy
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I believe, (would have to see it for sure) that the marks are in Mils. With that you can estimate range. A mil is a mil whether its 10 yards (or meters) or 10,000 yards (or meters).

Mils are used in Artillery and Machine Guns, (and now rifle scopes).

A mil is that angle whose tangent is 1/1000, that is the angle sutended by 1 unit at a distance of 1000 units. 1 yard at 1000 yards, or 1 foot at 1000 feet.

You can test this by getting a piece of string 20 inches long, tied to a target 1 inch wide. Hold one end of the string in your mouth and hold the other or pencil out. The range is 20 inches. The one inch target would be 50 mils.

So M or Mil = 1000*1/20 so M or mils = 50.

As a side note: Remember in basic we were taught to use fingers to estimate range. The average finger is 50 mils. You should also use your finger to cover an object. Looking at that object through your field glasses should measure 50 Mils.



Lets change this to a 1 yard target at 100 yards.

1000 * 1 / 100 = 10 so the 1 yard target would be 10 mils.

Knowing that, you can go the othe way. Lets say your 1 yard target is 10 mils. Range would be 1000*Target / Mils.

or 1000*1 yard / mils + range to the target. 1000*1/10 = 1000

Like any other math, if you know two of the 3, you can find the third.

Knowing this, you can play with your field glass and I'm sure you'll find out the marks are mils.
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