Hey Gang,

 

As many know I'm pretty new to shooting but hear a lot about 1 MOA accuracy but I haven't seen to much in terms of what that really translates into in terms of shot groupings at distance.

 

Does 1 MOA simply mean the "arc" covered by 1 minute of angle at a given distance?

 

Using that logic and some seventh grade geometry I get that 1 MOA at 100yds is equal to shot grouping of approximately 1.05 inches. Double that for 200yds and triple of 300yds.

 

My math works something like this:

 

Assume I'm standing in the center a circle with a 100yd radius or 3,600 inches.

 

Then 180 degrees of angle would be: 3600 x pi = 11,309.73 inches of arc

 

1 minute of angle would be (180 x 60)10,800 times smaller than that so 11,309.73/10,800 = 1.047"

 

I'm guessing in actuality a target is flat which would make the grouping a little smaller but in general you're looking at about an inch.

 

Is this correct or is there something more to it?

 

Thanks,

 

John

You are correct. Most shooters just round it to 1" at 100 yards, 2" at 200 etc etc.

Not the shooters I know Use 1.047. An MOA is 1/60th of one degree. That is an angle which subtends an arc whose length at 100 yards is 1.047 inches. A case for NOT using 1.047 is if your scope is calibrated in IPHY. And this is why I use mill . A mill is a mill. There are no different standards.

Insert here a big whine about scope manufacturers that calibrate their reticule in one unit of measure and their turrets in some other unit of measure.

Not the shooters I know Use 1.047. An MOA is 1/60th of one degree. That is an angle which subtends an arc whose length at 100 yards is 1.047 inches. A case for NOT using 1.047 is if your scope is calibrated in IPHY. And this is why I use mill . A mill is a mill. There are no different standards.

 

Except when it is not. Since there are tow things that are referred to as mils when talking about ranging.

 

http://www.mil-dot.com/articles/a-note-from-the-leupold-engineers

I think you are confusing mil dots with milradien. A mil dot is whatever the scope manufacturer/reticle designer say it subtends BUT its always on the same mil scale. So a mill is always a mil. Its one scale. MOA has a few different scales and reticles for those differences. Whats worse is when a scope manufacturer puts one scale in the ret and a different scale in the click value like Leupold did on certain models.

For example the mildot in my premier heritage 5-25 scope is .1mrad. A quick look at your link and it looks like they are using "Army" mills at .2 in the Leupold referenced. The Marine Corps uses football mills. But its all the same scale. In MOA you ned to know which scale your in because there are different scales. Frankly I dont care for the mildot as I range much more accuratly with hash marks.

 

And for those following along that wonder why it matters, that difference in inch per hundred yards vs true moa would equal about 18" for a 308 at 1000 yds. Thats a BIG difference.

Some links for those wanting to chase that rabbit down the deep hole.

 

http://static.scribd.com/docs/d2ke2aetnlp77.pdf

 

http://www.scribd.com/doc/4617008/Mils-and-Moa-Simplified

For example the mildot in my premier heritage 5-25 scope is .1mrad. A quick look at your link and it looks like they are using "Army" mills at .2 in the Leupold referenced. The Marine Corps uses football mills. But its all the same scale. In MOA you ned to know which scale your in because there are different scales. Frankly I dont care for the mildot as I range much more accuratly with hash marks.

 

And for those following along that wonder why it matters, that difference in inch per hundred yards vs true moa would equal about 18" for a 308 at 1000 yds. Thats a BIG difference.

 

Wouldn't the error at 1000yds be 10X the error at 100yds?

Yes.

i have a headache now, thanks Shane!

Hey Gang,

 

As many know I'm pretty new to shooting but hear a lot about 1 MOA accuracy but I haven't seen to much in terms of what that really translates into in terms of shot groupings at distance.

 

Does 1 MOA simply mean the "arc" covered by 1 minute of angle at a given distance?

 

Using that logic and some seventh grade geometry I get that 1 MOA at 100yds is equal to shot grouping of approximately 1.05 inches. Double that for 200yds and triple of 300yds.

 

My math works something like this:

 

Assume I'm standing in the center a circle with a 100yd radius or 3,600 inches.

 

Then 180 degrees of angle would be: 3600 x pi = 11,309.73 inches of arc

 

1 minute of angle would be (180 x 60)10,800 times smaller than that so 11,309.73/10,800 = 1.047"

 

I'm guessing in actuality a target is flat which would make the grouping a little smaller but in general you're looking at about an inch.

 

Is this correct or is there something more to it?

 

Thanks,

 

John

 

Or if you just think of a right triangle:

 

Tan(1/60)*100*3*12=1.04719"

ok so lets say your scope was calibrated in inches on the ret but the dials were in moa. So lets say that drop in inches @ 1000 for a 308 is 420 inches. Here is the formula

 

inches * 100

MOA = --------------------------

1.047 * distance in yards

 

That gives you 40.1 moa rounded. If you used inches per hundred yards you would crank in 42. That gives you a difference of 1.9 moa. If I did my math right thats 19.9 inches rounded at 1000yds of difference between the point of aim vs the point of impact.

ok so lets say your scope was calibrated in inches on the ret but the dials were in moa. So lets say that drop in inches @ 1000 for a 308 is 420 inches. Here is the formula

 

inches * 100

MOA = --------------------------

1.047 * distance in yards

 

That gives you 40.1 moa rounded. If you used inches per hundred yards you would crank in 42. That gives you a difference of 1.9 moa. If I did my math right thats 19.9 inches rounded at 1000yds of difference between the point of aim vs the point of impact.

 

 

Math is my weakest subject, but wouldnt the difference be the .047" difference at 100 yards, multiplied by 10 for 1000 yards, so you would only be off 0.47"?

Math is my weakest subject, but wouldnt the difference be the .047" difference at 100 yards, multiplied by 10 for 1000 yards, so you would only be off 0.47"?

No because you need to remember that moa is a degree of measure and not a fixed number. The further out you go, the bigger the spread. Very similar in concept to the bore choke in a shotgun and the way distance spreads out the shot pattern.

No because you need to remember that moa is a degree of measure and not a fixed number. The further out you go, the bigger the spread. Very similar in concept to the bore choke in a shotgun and the way distance spreads out the shot pattern.

 

It's because projectile drop is not linear function it is parabolic.

Math is my weakest subject, but wouldnt the difference be the .047" difference at 100 yards, multiplied by 10 for 1000 yards, so you would only be off 0.47"?

 

If you use 1MOA = 1.047inches at 100 yds. You get 1MOA = 10.47inches at 1000yds. The POA to POI delta (difference) is 420 inches. Divide 420/10.47 = 40.1 MOA.

 

If you use 1MOA = 1 inch at 100 yds. You get 1 MOA = 10 inches at 1000yds. Divide 420 by 10 and you get an MOA of 42.

 

A difference of 1.9 MOA Which at 1000yds = 1.9 x 10.47 = 19.9 inches.

 

The parabolic path of the bullet affects where it will hit and gives us the delta between POA and POI.

Ooof the formula looks all twisted in the post.

 

 

moa = inches X 100 devided by 1.047 X Distance in yards.

 

moa = 420 X 100 / 1.047 X 1000

 

moa = 42000 / 1047

 

moa = 40.1

Ooof the formula looks all twisted in the post.

 

 

moa = inches X 100 devided by 1.047 X Distance in yards.

 

moa = 420 X 100 / 1.047 X 1000

 

moa = 42000 / 1047

 

moa = 40.1

 

You're right. Let me go edit my post. I can't read my calculator.

Why are you guys taking bullet drop into the equation? It really has nothing to do with MOA accuracy. Or is that not what we are talking about?

 

Knowing your range and knowing your bullet drop and knowing the capability of your rifle should be all you need. The thing that generaly throws me is calling wind drift and that generaly takes me a 1 or 2 shots(Thank God my life doesn't depend on it)

 

Please explain.

 

FS

Why are you guys taking bullet drop into the equation? It really has nothing to do with MOA accuracy. Or is that not what we are talking about?

 

Knowing your range and knowing your bullet drop and knowing the capability of your rifle should be all you need. The thing that generaly throws me is calling wind drift and that generaly takes me a 1 or 2 shots(Thank God my life doesn't depend on it)

 

Please explain.

 

FS

 

The OP expressed an interest in learning more about the math behind MOA. If you know bullet drop and range, you can calculate your error between point of aim and point of impact in terms of MOA and then make the proper adjustments. You may have already figured out a short cut that let you go right from error to adjustments without worrying about MOA.

The OP expressed an interest in learning more about the math behind MOA. If you know bullet drop and range, you can calculate your error between point of aim and point of impact in terms of MOA and then make the proper adjustments. You may have already figured out a short cut that let you go right from error to adjustments without worrying about MOA.

 

 

Thanks, I see... It may be the proper way to establish POA/POI.

Using an actual example makes it easier to understand the concept imo and better illustrates why the error matters.