If I could see some kind of a drawing of this I think it will help me immensly. Thanx

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If I could see some kind of a drawing of this I think it will help me immensly. Thanx

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It's that geometry class we barely remember back in high school.

Is odd that every other number system modern man is use to is based on 10 but our clocks are based numbers that easily divide into 360 (or you can say base 12 if you like). Seems like we took that same system for geography as well (longitude and latitude are figured in degrees. minutes, seconds as well).

(Want to get a confused look when some one asks what time it is? If it's 3:40, tell them it's "a third to 4".)

As you stand in once place and turn in a circle, you've covered 360degrees. We have a pretty good mental handle on big angles, like 45degrees or even a 2 or 3 degree slope. It's the little ones we have trouble visualizing.

Each one of those 360 degrees can be divided into minutes. Each of those minutes can be divided into seconds.

In shooting, we've come to round off the value to 1" at 100 yards. It really works out to be a little bit more than 1" at 100 yards. As it is an angle, then it's worth is proportional to distance. 1/100th at 1 yard, 1/10th at 10 yards, 1/2 at 50, 1 at 100, 2 at 200, etc.

So if you stood there and pounded in stakes at 1000 yards that were 10 inches apart, tied 1000 yard strings onto them, and lead the strings back to where you stood so that the strings crosssed at your foot, that would be a visual of 1 minute of angle.

Jim

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103 Posts

on the line of the circle after aiming at a mark in center of circle.. you shot moa..assuming a hundred yrd is the distance..then unless wind is a factor,you can adjust sight in for better results..right left ,up or down..

if shooting groups ,its measured center of impact to center of impact..

hope i didn t misinform..

mabe i ll learn something,, if this is wrong an i ll understand it better from following posters..

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674 Posts

What?

on the line of the circle after aiming at a mark in center of circle.. you shot moa..assuming a hundred yrd is the distance..then unless wind is a factor,you can adjust sight in for better results..right left ,up or down..

if shooting groups ,its measured center of impact to center of impact..

hope i didn t misinform..

mabe i ll learn something,, if this is wrong an i ll understand it better from following posters..

You didn't read ribbonstone's post did you?

There are 360 degree's in a circle.

There are 60 minutes in a degree.

At 100 yards that minute measures out to 1.05 inches

Any group that measures smaller that 1" will be under MOA and any group over MOA is more than MOA. It is that simple.

Minute of arc is a lesser used term but actually describes it better and it is the same exact thing.

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It doesn't take a very big change in sight line and bore line angle to move the bullet a significant distance at most common shooting ranges. For that reason, a very small measure of angle needs to be used to adjust sights. The moa (1/60 of a degree) is the conventional choice. We could have used milliradians (as mil dot sight reticules do) and it would have made more sense mathematically and allowed a common unit system to be used for both rifle and artillery, but moa is the historic unit of measure of the adjustment angle for all small arms sights, so it is the unit our sight settings use.

The illustration below uses an exaggerated angle to provide the distance measures. As I said, above, the sides of the 1 moa angle get further apart the further you go forward of the gun. By the time you get to 100 yards the are very close to pi/3 inches apart (1.0472… inches). That means that at 100 yards a 1 moa change in sight setting will move the point of impact pi/3 inches. If the target was at 200 yards, that same 1 moa sight adjustment changes the point of impact 2×pi/3 (2.0944…inches); by the time you get to 300 yards that same 1 moa adjustment moves the point of impact pi inches (3.15159… inches); etc., etc.

The above is why the adjustment is often said to move the point of impact 1.05" per hundred yards of distance from the target. 1.05" is close enough to the exact number that the shooter won't ever see the difference. It's less than 0.03" of error at 1000 yards; too small to hold the rifle to, and even if you could, it is too small not to be overwhelmed by shot-to-shot velocity variation and atmospheric irregularities.

Note that if you rotate the sight on its axis, the sides of the angle describe a cone, with a circle 1 moa across on the target. When you hear people say they have a 1 moa group, the shots staying inside that circle is what they mean.

Bryan Litz, in his book, Applied Ballistics for Long Range Shooters, says a lot of sights fail to move the sight line the exact number of moa per click the makers claim. Some adjustment mechanisms and optics don't move the same amount per click either side of the center of the adjustment range. Some don't move it the same amount per click near the center that they do near the ends of the range. For a small adjustment you don't notice the error, but for that 30 moa shift needed for 1000 yards, the cumulative error can be pretty far off. There is also the problem with iron sights that are the same, but placed on different barrel lengths where the front and rear sights are different distances apart.

Litz recommends strongly that you measure what your sights do. He sets up a target with a straight line about a yard tall vertically above a bull. You can make your own by putting a standard target at the bottom of a tall cardboard backer and just drawing the line on it with a yard stick. You zero the rifle on another target. When you have that, you put up your tall target and fire a group into the bull. Adjust the sights up 1/4 of the total adjustment range and fire another group. Repeat at half, three quarters, and full vertical adjustment. Find the centers of the groups and measure how far apart they are. That will show you what your adjustments are doing. Divide the distance between each group by pi/3 to see how many moa the group actually moved. Divide the result by the number of clicks of adjustment you used to see how many moa each click of your sights really is in that part of the adjustment range.

In the above text you'll note I said the separation was "about" pi/3" per hundred yards. For the sake of mathematical exactness, the target is a plane and pi/3 is the length of the 1 moa arc at a radius equal to the range, and is not the straight line length that subtends that angle at 100 yards. However, the angle is so small, the arc doesn't have much bend over that short distance, so the difference in its length and the length of a straight line across the diameter of the sides of the angle, is only about 0.00000000397 inches at one hundred yards, and is, again, ignorable. Even elevating a sight 30 moa to shoot at 1000 yards, the error is only about a ten thousandth of an inch. Nothing the gun or shooter can detect.

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An MOA group therefore, is an inch at 100 yards, two inches at 200 yards, three inches at 300 yards ... and 176 inches at one mile. (Yes, a one MOA rifle will shoot a 14-FOOT group at a mile under perfect conditions.)

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ummm, ah-ha -- may we remind you that absolutely none of this discussion is about combat? Nor should it be. There may be websites where such blather is welcome, but it isn't this one. (Modrerators forgive me for encroaching on your turf.)

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So Unclenick, bending my target backers at 100 yards is pretty much useless?

Luis

Luis

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103 Posts

you are sure nuff right grump..

These days, every guy with enough money to buy a gun and a computer finds an MOA just about every time he pulls a trigger. Oddly enough, there has never been any correlation between finding an MOA and successfully hunting more edible creatures, like deer and elk, even though a lot of guys that are still wet behind the ears will try and tell you ya can't hunt anything unless you find an MOA first. Pure hogwash.

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As the post has already drifted off topic, I expect there are non-participating readers now wondering when understanding sights matters and who are not familiar with all the shooting sports and games. There are a number of multiple range matches that allow no sighters (the National Match Course, for one, and a lot of tactical rifle and even buffalo rifle silhouette matches for a couple more examples). As a result, target shooters find knowing how to determine ranges and come-ups and windage for their particular sights is pretty important. Jim Owens has a book on how people screw up sight adjustments even when they do have sighters and do know what change their sight clicks make, so this is a big deal to match scores and involves some unexpected subtleties. Laser range finders are making that kind of knowledge more useful in the field all the time. At long range a correct sight adjustment can save you spooking grazing game with a near miss.

For those critical of the need to understand sights and settings, I recommend you take a long range shooting class or a sniper or tac rifle class. You'll have fun and learn some new possibilities.

Luis,

A couple of times in indoor bullseye matches, where the backer and target were just hanging from a clip, I let the last round go late as the target turned edgewise, and the bullet cut both the backer and target in half. Not too helpful to your score to have the bottom halves drop to the floor. Usually gets a good laugh.

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