Can someone explain MOA?

[Cheeseybacon]

OKay folks, this is somewhat embarassing. Maybe I just suck at math really bad (actually that's not a maybe I KNOW I suck at math, heh), but I am having the damnedest time understanding the entire concept behind MOA as it is related to rifle accuracy.

The basic explanation I read from Wikipedia says that under ideal conditions a 1 MOA rifle should be capable producing 1" groups at 100 yards, and thus a 2 MOA rifle should be capable of 2" groups at that same 100 yards. OK, that's fine, that part I get.

What I am having trouble understanding is: What kind of groups are theoretically possible if a rifle is rated at 1 MOA accuracy at a distance MORE than 100 yards? Then what? Do they still mean 1 inch groups but at 1000 yards? Or is there some mathatical trickery and whatnot that is involved in determining what size group the rifle is theoretically capable of? Like 1 MOA @ 100 yards = 1 inch group, but 1 MOA @ 1000 yards = 10 inch group? Am I heading in the right direction at all?

The reason why I ask is because there is an AR-upper in .50 BMG that I'm looking at and they're saying in their FAQ that 1 MOA accuracy at 1000 yards is possible with good ammo. I was just curious what exactly they mean by that.

Can anyone explain this to me better? My brain is mush today, and I'm a little cornfused...

Edit: Hmmmmm, perhaps I should have posted this in the rifle forum instead.

[SSCUSTER]

You are correct in your math that 1 MOA at 1000 yards would be a 10" group. However, if you and your rifle can shoot 1 MOA at 100 yards, you are not guarenteed 1 MOA at 1000 yards.

Thare are a lot of forces acting upon that bullet while it travels the remaining 900 yards. Average velocity, friction, gravity and wind are but a few variables. I'm not going to pretend that I know all of the physics involved or that I am a 1000 yard shooter. I just know it is not as straight forward as it appears.

[jsb889]

When they say 1 MOA at 1k yards, it means 10 inches at 1k yards. You pretty much have it. A 1 MOA rifle, theoretically, shoots 1 inch at 100 yards, 4 inches at 400 yards, 6 inches at 600 yards, 7.5 inches at 750 yards. A 2 MOA rifle does 4 inches at 200 yards, 20 inches at 1k yards, 10 inches at 500 yards.

Whats your scope sight in procedure for long ranges? Thats where it gets pretty confusing, took me a little while to understand that part .

[Philadelphia]

What you've got is a triangle with equal length sides (distance between gun and target) with the base being group size. The angle formed by the two equal length sides is that minute of angle. A full circle is 360 degrees, each degree has 60 minutes and each minute has 60 seconds. So one minute of angle = 1/60th of a degree.

To get the group size, divide your triangle down the middle into two right triangles. (which halves the angle and calculates half the group size). The formula for group size for a one minute of angle would then be . . .

Sine(1/120) X distance to target X 2

Don't forget that if your distance to target is in yards, your group size will be calculated in yards -- convert back to inches (miltiply the result by 36). Using the above formula, a 1 MOA gun produces a group slightly over 1 inch.

At 1000 yards, 1 MOA equals slightly over 10 inch group (around 10 and a half inches). The group size is proportional to the distance to target.

[Cheeseybacon]

I'm sort of a visual learner, so I tried my best to visualize this in a completely-to-scale, high-precision drawing using a MS Paint.

If for some amazing reason my brief reunion with high school trigonometry is indeed correct, my calculations tell me that the path of the bullet would not be able to deviate more than 0.0015 degrees upon exiting the barrel in order to be within 1 MOA at 1000 yards. Does this make sense at all?

Does it even matter? Probably not. Am I thinking about it too much? Definitely. Should I even bother buying a .50 BMG upper? I don't know!!!

[DaveM55]

http://www.snipercountry.com/Articles/MilDot_MOA.asp

[vetter3006]

I'm sort of a visual learner, so I tried my best to visualize this in a completely-to-scale, high-precision drawing using a MS Paint.

If for some amazing reason my brief reunion with high school trigonometry is indeed correct, my calculations tell me that the path of the bullet would not be able to deviate more than 0.0015 degrees upon exiting the barrel in order to be within 1 MOA at 1000 yards. Does this make sense at all?

Does it even matter? Probably not. Am I thinking about it too much? Definitely. Should I even bother buying a .50 BMG upper? I don't know!!!

Great graphic, thanks

[knight0334]

MOA = 1/60 of a degree
360 degrees in a circle

At 100yard(300ft), the circumference of a circle is 1884'(D*Pi).
(Pi rounded to 3.14 for simplicity)

1884' = 22608"

22608"/360 degrees = 62.8

62.8/60 minutes = 1.04666667" = 1 Minute Of Angle @ 100yrds

[markheck1]

yep, that's the technical explanation....

the layman's explanation is 1 inch groups fr every hundred yards, all things being equal....but alas they are not......as was mentioned before, the shooter, wind, bullet velocities..etc...

That is the expectation by the way, of a Marine Scout Sniper.....

as to the other question....there's 2 ways

1) bullet drop compensator scope calibrated to your bullet......

2) and the most accurate, and the most fun by the way, is trial and error.....if you plan on doing this at a lot of different ranges, it's best to have target turrets on your scope....sight in at 100, then shoot at 200 and move scope until centered..record number...shoot 300 and move scope till centered....record number....you get the picture.

BTW with option 1 it should still be tested......

[jsb889]

Very nice graphic. You got it