What is MOA?

[ar15barrels]

Look at a small object near you. And the object or spot on a wall across the room behind it.

Shuffle to the left or right. And look at the small object, and whats behind it...

The object, (substitute for a reticle) never moved, but your eye did. And whats lined up behind the object has shifted.

In my case, sitting in the living room.... looking at the little 'fob' on the chain of the ceiling fan, and the spot on the ceiling behind it. Move my head to one side.... the spot on the cieling behind it moves too. Imagine, that fob was the reticle of a rifle scope- bagged in solid position that doesnt move. That shift in eye placement shifts the target you see.

Even setting parallax this will happen. It will significantly reduce the error, but there is still error induced from it.

Proper adjustment of parallax removes ALL parallax error.
The markings on the knob are rarely correct.
Set parallax by bobbing your eye around behind the fixed gun/scope and groups will improve, significantly.
A misunderstanding of parallax is probably one of the biggest factors keeping most shooters from shooting better groups.

[ar15barrels]

what you say about vertical stringing doesnt make sense to me.... I dont get how closer or farther to the sight would change elevation.

It changes HOW the gun moves during the time that the bullet is moving down the barrel.
A zeroed rifle takes into account the amount of movement during the bullets travel down the barrel.
That is why zeroing a rifle is a personal thing.
A rifle moves differently in recoil when I am behind it than when you are behind it.

This is also why you zero the rifle in the method you intend to shoot it most.
I zero my longrange guns in prone with a bipod and rear bag.
I zero my hunting guns sitting up and shooting over a pack.

[koxx.dta]

i understand moa as in 1" for 100 yards but what does this mean with a red dot that says 3 or 4 moa? 4moa red dot would cover 4" of the target at 100 yards?

[Pthfndr]

i understand moa as in 1" for 100 yards but what does this mean with a red dot that says 3 or 4 moa? 4moa red dot would cover 4" of the target at 100 yards?

Yes.

[postal]

Interesting.... Thanks Rob, Randall for straightening me out.

1 thing though.....

As to marked parallax settings on a scope, and not being correct... I just found out through personal experience, if you change the fast focus eyepiece, it throws off the marked distance.

I setup a new scope against a blank white wall and adjusted the focus to get the crosshair nice and crisp.... The parallax was WAY OFF.....

Looking at a target at 100y, and setting the knob at 100, adjusting the focus until it's parallax free, is where I left the focus. I figure the ease of quickly dialing distance for parallax was more important than a crisp reticle.

Of course I could go to adjusting the eyepiece and marking the parallax knob for correct distances. Which I'll do during the down season.

[CK_32]

MOA is Minute of Angle = 1" @ 100 yards.

2" @ 200 yards. Ect.

A common misconception is the measure out side to out side of the holes and call it a day which isn't true. You measure from middle to middle of the holes or out side to out side and divide by the caliber of bullet .308, .223 ect. That is how you read MOA or groups.

Being 2 pages long I'm sure that's been answered and there is a huge pissing contest or it's just veered off topic. Either way that is what it is. Hope it helps.

[Pthfndr]

You measure from middle to middle of the holes or out side to out side and divide by the caliber of bullet .308, .223 ect. That is how you read MOA or groups.

No, you subtract the bullet caliber diameter.

[JMP]

Milliradians or "mils" is based on taking a complete circle then subdividing it into 1000 equally sized pie pieces. 1 Mil is about 3.5 MOAs or 3.5"

Radian are measured as the ratio of arc length to radius.

The circumference of a circle is 2 * pi * radius

Thus, the number of radians in a complete circle = (2 * pi * radius)/(radius) = 2 * pi.

An MRAD is 1/1000 of a radian.

So, there are actually 2 * pi * 1000 ~ 6283 MRADs in a complete circle.

100 yards = 3600 inches, so the distance is Tan(1/1000) * 3600 = 3.6"

It works much better in the metric since it is a base 10 system.

So, Tan(1/1000)*100 meters = 0.1 meters, or 10 cm @ 100 meters, so each 0.1 MRAD click = 1.0 cm @ 100 meters.

[xrMike]

Being 2 pages long I'm sure that's been answered and there is a huge pissing contest or it's just veered off topic.

Amazingly, no. A rarity on Calguns these days.

[postal]

Amazingly, no. A rarity on Calguns these days.

...Oh.... dont get me started!!!!

Kidding! just kidding!!!! Funny as heck though!

[ar15barrels]

No, you subtract the bullet caliber diameter.

Its actually more accurate to subtract the diameter of a single lone hole on the exact target as the target paper stretches open as the bullet goes through it.
You will often find that a single bullet hole measures 0.025" smaller on the target paper than the bullet that made the hole.
Say you measure a group as 1.000" outside-outside and you subtract 0.308" bullet diameter.
That leaves you a group size of 0.692"
Then you measure a single bullet hole and it measures 0.280".
Since you are measuring the group with the same measuring method, both values will have similar accuracy/inaccuracy of measurement.
The 0.280" measured hole subtracted from the 1.000" measured group gives a more accurate group size of 0.720"...

[Pthfndr]

Its actually more accurate to subtract the diameter of a single lone hole on the exact target as the target paper stretches open as the bullet goes through it.
You will often find that a single bullet hole measures 0.025" smaller on the target paper than the bullet that made the hole.
Say you measure a group as 1.000" outside-outside and you subtract 0.308" bullet diameter.
That leaves you a group size of 0.692"
Then you measure a single bullet hole and it measures 0.280".
Since you are measuring the group with the same measuring method, both values will have similar accuracy/inaccuracy of measurement.
The 0.280" measured hole subtracted from the 1.000" measured group gives a more accurate group size of 0.720"...

Yeah, but then group size isn't as small. What fun is that when one is posting a cherry picked picture

My groups are never small enough that 25 thousandths of an inch is going make an impressive difference anyway

[sjb269]

Dammit! Google must be broken again!