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Old January 15, 1999, 01:45 AM   #1
Jeff Thomas
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I understand that MOA (minute of angle) means that at 100 yards your shots are in a 1" group, at 200 yards in a 2 inch group and so on. After that, I'm lost.

Did this term originate in the military? Or, is it a term from target competition?

Is 2 MOA a 2 inch group at 100 yards? And, if a gun shoots MOA, does that mean all shots are within a 1" group, on average they're in a 1" group, or ??

I would think the weapons that fire MOA are fairly rare and expensive - seems like a hell of a feat when you're used to being a 'plinker'.

Thanks.
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Old January 15, 1999, 03:05 AM   #2
pat
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i dont know who first used the term but in geometry there are 360 degre in a circle then each degree is broken into 60 min each of 60 sec as the trig works out 1 min of a degree in angle at 100 yards is almost 1 inch and at 200 it would be 2 inch and so forth just as 2 min is two inches at 100 and 4 at 200 hope this helps
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Old January 15, 1999, 03:07 AM   #3
pat
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cont. so a 1/4 min sight moves the bullet flight path 1/4 min of angle for each click resulting in a 1/4 inch change in impact point for each click at 100 yds
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Old January 15, 1999, 06:40 AM   #4
Harley Nolden
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MOA in standard hunting rifles can be achieved in many rifles. It does take some time and effort.

1. Marry the ammo to the gun.
Not all ammo performs well in every rifle. It is a matter of trial and error. Using different mfg'd ammo, recording the MOA and finding which one fires better in your gun. This will include bullet weight also.

2. Glass bedding:
Bedding the recoil lug will improve the MOA noticabley.

3. Reliving the barrel channel where ever it touches the barrel. "They" say if you can slide a dollar bill, between the barrel & forearm, you have a floating barrel. On a hunting rifle this will work.
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Old January 15, 1999, 12:59 PM   #5
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Minute of angle is 1.047" at 100yds. GLV
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Old January 15, 1999, 02:38 PM   #6
Michael Carlin
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Pat has the definition and GLV (hi George) has the measurement for 100 yards.

As Pat indicates a Minute is 1/60th of a degree and we all Know that a circle has 360 of those.

SO:

360 degrees X 60 minutes per degree equals 21,600 minutes in a circle.

The circumference of a circle equals Pi X Diameter or 3.14 X Diameter

Diameter(equals 2X [the radius for a 100 yard MOA] (100 yards X 36 inches)= 7200 inches)

So.. 3.14 X 7200 = 22608 inches around a circle of 200 yards in diameter.

The circumference of 22608/21600 minutes in a circle = 1.047" subtended by an angle of One minute at a radius of 100 yards.

Hence:
One Minute of Angle = 1.047" at 100 yards
One Minute of angle = 5.233" at 500 yards

One Minute of Angle = 10.47" at 1000 yards


No mystery here, just simple geometry.

Hope this helps!


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Old January 15, 1999, 04:13 PM   #7
olegunftr
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you go dude!!! you know what is scarry, an Abrams M1A1 tank with 120mm gun can shoot beter than an MOA way, way out there.

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[This message has been edited by olegunftr (edited 01-15-99).]
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Old January 15, 1999, 04:32 PM   #8
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Jeff: One other item in this is that group sizes are measured from center to center, not the distance from the outer edge of a bullet hole across to the farthest outer edge. It's just another convention which began Lord knows how many decades ago.

Another generalization is that a "one-minute" rifle reliably averages such a group (sometimes the jerk behind the trigger jerks the trigger), and the "standard" group is five shots.

Forty or fifty years ago, one MOA was regarded as really great in a hunting rifle. Today's precision machining makes it halfway commonplace.
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Old January 16, 1999, 12:28 AM   #9
Michael Carlin
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Art, Jeff

The easiest way to get a center to center measurement, which is correct Art, is to measure the group at it greatest dimension and subtract from that measure one bullet diameter.

So a group that measures 2.378" overall (outside to outside) shot at 200 yards with a 7mm would be exactly 1 MOA or 2.094" center center of the farthest apart shots. (2.378 - .284 = 2.094)

Art, it is true that the convention for rifles is 5 shots, but I really believe that a 10 shot group is much more revealing about the true character of the load.

A twenty shot group is even better but you have to draw the line somewhere.


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Old January 17, 1999, 12:16 AM   #10
Art Eatman
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Michael: Definitely yes, the ten-shot group is a better indicator. The only utility to the five-shot group as the indicator is that 90% (I guess) of all rifles are predominantly used for hunting, and after three shots, what's the point?

We should move this thread to "...Rifle?"
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Old January 17, 1999, 09:55 AM   #11
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Art-
Thanks for giving the move a thought. The thread's well underway, so it won't hurt to leave it here.
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Old January 17, 1999, 11:40 AM   #12
Jeff Thomas
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Thanks to everyone for clarifying this topic so well. [my geometry is pretty rusty - Michael, you're giving me a good refresher! ]

And, I apologize if I've placed this topic incorrectly - I understand why Rich wants to keep this forum well organized, and I'll do my best to cooperate. On the other hand, while MOA would usually be used regarding rifles, wouldn't it also apply to pistols, and perhaps even theoretically to shotguns firing slugs? It is a general concept of firearms accuracy, no? As olegunftr pointed out, it seems this concept would even apply to an M1A1.
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Old January 17, 1999, 05:50 PM   #13
Rich Lucibella
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Jeff-
You're quite right. We've even seen it applied to Artillery here. since Patton is dead, I don't have a lead for Forum Moderator on that one.

The thread is fine...and worthwhile. Please carry on.
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Old January 17, 1999, 07:25 PM   #14
Jeff Thomas
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Rich - thank you. And, if we have any BATF lurkers here, I promise, cross my heart, I have no interest in obtaining an M1A1. Besides, I hear you can't get any pre-ban hi-cap mag's for those anyway ...
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Old January 17, 1999, 11:55 PM   #15
Art Eatman
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BATF won't let me have an M1A1? And I've got a place to play with one! $#%$@#!

Jeff, the main reason for worrying with MOA is for "long range" rifle accuracy, generally looked at as 100 yards and on out (older days) to today's 400 yards or so on to 1,000 yards.

Nothing would keep you from using MOA in talking about handgun-accuracy. Since few people duplicate Elmer Keith's accomplishments--or try to--it's not really germane to the discussion. Look in our forum on handguns, and folks talk about an inch or two at 50 yards for group size for accurate pistols, with a few shooting into half that size. I guesss it's a "why bother?" sort of thing...

Now, some of the stuff going on with the TC world is "a whole other story" from the revolver and pistol world.

Historically, MOA is a rifleman's term...

Hope all this ancient history helps. Like a lot of stuff in the world of shooting, it's inherited conventions...[What am I, the History Channel? :-)]

Regards, Art
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Old January 23, 1999, 04:41 PM   #16
Jeff Thomas
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I want to say thanks again for a very helpful thread. This is hopelessly anal, but I took some of the geometry outlined above, and created an Excel spreadsheet. Not terribly useful, but forced me to work through the math, and understand exactly what this term means. For me, there is a difference between simply defining the term versus working the math and visualizing the concept.

So, if I'm ever at the range, and I find the target is only 99 yards out, I'll know that the MOA is only 1.0367 Adios.
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Old January 25, 1999, 08:36 AM   #17
Michael Carlin
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Jeff,

Glad to see another "hopelessly anal" person work the math.

Man, if my geometry, trig, and calc teachers had only said, "Look here Carlin, you can calculate the come up for 600 to 1000 without firing a shot and be in the ball park!" I wold have been a much better student!



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Old December 19, 2011, 05:39 PM   #18
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I've been trying to wrap my head around this MOA concept for a while now, starting with the geometric principle and then trying to relate it to marksmanship. I was shown at a young age how scopes can be adjusted using 'clicks' (nice having a dad working as a sharpshooter with the RCMP's ERT team Most common scopes seem to be set up as 1 click = 1/4 MOA, some at 1/8...

What I could really use is some practical instruction or demonstration relating this principle to marksmanship. Should I join a rifle club? And if so, would MOA be their standard of accuracy measure? Or are there any good videos online? I'm generally a learn-by-doing type so the theory has gone over my head a little.

Also, as Jeff mentioned above, it's definitely a bonus knowing how to adjust your scope for different ranges without first firing a shot. Does this require making a drop chart for a specific rifle?
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Old December 19, 2011, 07:27 PM   #19
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If you have trig functions on your calculator

tan^-1(group size ÷ range) x 60 = MOA

Your calculator may mark the arctan function “arc” or even arctan.

It is imperative that the units used for group size and range be the same, so if the group is 1.5 inches in diameter, the range must be 3600 inches, not 100 yards. For that 1.5 inch group the calculation is:

tan^-1 (1.5÷3600) x60=1.4 MOA (yah, yah, 1.4324 etc. but sig figs!)
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Old December 19, 2011, 07:37 PM   #20
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Quote:
What I could really use is some practical instruction or demonstration relating this principle to marksmanship. Should I join a rifle club? And if so, would MOA be their standard of accuracy measure? Or are there any good videos online? I'm generally a learn-by-doing type so the theory has gone over my head a little.
The usual standard of accuracy is group size. Some express this as MOA. When a firearm is said to shoot "sub-MOA" all that means is it will shoot a group smaller than 1-inch at 100 yards.

Group size is, IMHO, easier to visualize. I have a mil-surp Mauser. Using mil-surp ammo I can shoot 4-inch groups at 200 yards. That can be expressed either as 4" groups, or 2 MOA.

The difference is that MOA is an angular measurement that is always the same angle, regardless of distance. Group size is meaningless if you don't know the distance. 4 inches at 200 yards isn't a great group to a world-class high power rifle competitor, but it's not horrible for an inexpensive mil-surp rifle using inexpensive mil-surp ammo. 4 inches at 500 yards would be superb. 4 inches at 100 yards would be borderline sucky, and 4 inches at 50 yards would be outright terrible.

But 2 MOA is always 2 MOA, at 50, 100, 200 or 500 yards.
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Old December 19, 2011, 08:52 PM   #21
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It's called dispersion, measured in minutes of angle ,conveniently - 1 MOA @ 100 yds is almost exactly 1".
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Old December 20, 2011, 03:21 AM   #22
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Except for top tier marksman, most firearms shoot better than the operator.

A number of writers and testers have reported rifles and loads that shoot smaller spreads at longer distances than at shorter ranges.

Example writer ___ reports that factory Xs ammo shot 1.5 inch group at 100 yds, 1.75" at 200 yds and then opened up to 3" at 300 yards.

Is this rifle a sub minute rifle, and over minute rifle, or a minute rifle?

In the end do you hit what you are shooting at and does it put the target on the ground.
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Old December 20, 2011, 03:29 AM   #23
maestro pistolero
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Quote:
One Minute of Angle = 10.47" at 1000 yards
Just under 1/2 deviation even at 1000 yards! This illustrates why using 1 inch @ 100 yards is close enough for just about any civilian work. Still, my first serious scope is in mils. No deviation whatsoever. Great thread.
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Old December 20, 2011, 05:31 AM   #24
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Quote:
... The easiest way to get a center to center measurement, which is correct Art, is to measure the group at it greatest dimension and subtract from that measure one bullet diameter. ...
But of course some of us can't leave it that simple. Lately I've been subtracting the average size of the two holes I'm measuring from, since the holes are rarely the exact diameter of the bullets. They can vary from one type of paper to another and even from one hole to another on some paper. Now that I've finally gotten under .5 MOA it can make a noticeable difference. And I use calipers now too, so I can get 100ths of an inch, or 1000ths if I ever feel the need. Probably won't need the 1000ths this year or next. But digital calipers sure make short work of it.

Flops
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Old December 20, 2011, 02:20 PM   #25
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The easiest way to get a center to center measurement, which is correct Art, is to measure the group at it greatest dimension and subtract from that measure one bullet diameter.
Unless you are shooting wadcutters the bullet holes are not all that likely to be one caliber to 0.001 inch tolerance.


Quote:
tan^-1(group size ÷ range) x 60 = MOA...

tan^-1 (1.5÷3600) x60=1.4 MOA (yah, yah, 1.4324 etc. but sig figs!)

More than significant figures, an approximation.

You can get the correct answer by dividing the group size by 2, computing the angle,and then doubling it.
MOA is not a perpendicular concept, but a circular measurement.
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