What is M.O.A.?

Put simply, M.O.A. stands for Minute of Angle and is an angular measurement that equals 1/60th of a degree.
At 100 yards, 1 M.O.A. = 1" (Technically 1.047")
At 200 yards, 1 M.O.A. = 2"
At 300 yards, 1 M.O.A. = 3"
and so on.

We often receive calls where customers request a 20 M.O.A. base because it is taller. 20 M.O.A. does mean that your rail will be slightly taller than a 0 M.O.A. rail, but it is not by much. In reality, our 20 M.O.A. bases are typically around .030" taller depending on the length of the base. That is less than half the thickness of a quarter. If you are looking to have your scope sit higher off of the receiver, we recommend using a set of medium rings.

Note the .030" difference in the rear of the bottom mount.

A 0 M.O.A. base is effectively a rail that is parallel to your firearm's barrel. There is no built in elevation. Scopes come with varying amounts of elevation adjustment, commonly M.O.A. and M.R.A.D. We use M.O.A. as our unit of measurement. If a scope has 60 M.O.A. of elevation adjustment (up and down), when mounted on your rifle with a 0 M.O.A. mount, it should end up close to the middle of that adjustment range when zeroing at 100 yards.

Vortex has a great video explaining why scopes aren't always zeroed exactly in the middle of their elevation range.

Here is the basic equation.

30 M.O.A. up + 30 M.O.A. down = 60 M.O.A. total in your scope.

A general rule of thumb that we use for simplicity is, if you are shooting from 0 - 500 yards, we recommend a 0 M.O.A. rail. This should allow you to zero your firearm at 100 yards and dial shots out to 500 yards. (There are certain times when this doesn't apply, like when you have a rimfire rifle!)

If you are looking to push past 500 yards, and are OK zeroing your scope at 200 yards, we recommend a 20 M.O.A. rail. Depending on how much internal adjustment is available in your specific scope, you may or may not be able to dial back to 100 yards. For example:

Let's use the scope with 60 M.O.A. total elevation adjustment as an example. We now know that with a 0 M.O.A. rail, you would have 30 M.O.A. of up travel and 30 M.O.A. of down travel when zeroing at 100 yards. When you place that scope on a 20 M.O.A. rail, the scope is now pointing down 20 M.O.A. because of that elevation in the rear of the scope mount. Now, when you center your scope on the target at 100 yards, your rifle will shoot 20 M.O.A. high (20 inches at 100 yards).

You will still have 60 M.O.A. of travel in your scope, but you will have effectively removed 20 M.O.A. from the top and put it on the bottom of the elevation range. To zero your scope at 100 yards with a 20 M.O.A. base, you will have to adjust your scope's elevation up by 20 M.O.A., but this can be an issue with only 60 M.O.A. of total elevation.

Now your equation will look like this:

10 M.O.A. up + 50 M.O.A. down = 60 M.O.A. total in your scope.

This will only allow you 10 M.O.A. of up adjustment (if you are zeroed exactly in the middle of the scope's range from the beginning). Being this close to the end of your scope's elevation adjustment range could also be putting unnecessary stress on your scope's internal components. If you are looking to zero your scope at 100 yards, we typically recommend having at least 65 M.O.A. of internal adjustment.

Which M.O.A. do I need to purchase?

We recommend 0 MOA for shorter distance shooting (0-500 yards). See your scope manual to determine the amount of elevation adjustment or range you have. For long distance shooting we recommend 20 MOA (500-1000 yards). The 20 MOA angled downward mount will allow you to see and zero where your bullet will strike over a long distance like 1000 yards.

How far will Zero or 20 M.O.A. allow me to shoot?

0 MOA is generally used for shooting 0 – 500 Yards depending on your scope and caliber
20 MOA is generally used for shooting 500 – 1000 + yards depending on your scope and caliber
At 100 yards, one MOA is about 1" (slightly more)
The scope mount cants downward at 20 MOA, which will allow you to zero your gun at a greater distance.
We typically recommend zeroing a rifle with a 20 MOA rail at 200 yards.
Most of the time you will not be able to zero a gun with a 20 MOA rail at 100 yards.
At 600 yards, a 20 MOA mount will point the scope down .120” or point the barrel up depending on your perspective.
One MOA = 1" at 100 yards or 6 inches at 600 yards. 20 MOA = 200 inches at 1000 yards.