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Old 12-29-2013, 09:56 AM
Davcruz
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Explain MOA rails to me please



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So I am new to the "details" of rifles and guns. I have always been kind of an "out of the box" shooter for fun. That said, I found a deal on a used 10/22 not that long ago and it was "done up" a bit by the PO. I have kinda gotten the bug to take my shooting a bit more seriously and of course the best way to get better is to understand the tool you use! The rail on it is stamped 15 MOA. I have seen folks here and on perfect union mention other rails like 25 MOA for example. What is the purpose of these different "MOA" rails?
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Old 12-29-2013, 10:15 AM
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Purpose? Kind of mixed up with the "how." Short version: they prop up one end of the scope. The rail is a wedge shape rather than flat -- one end is thicker than the other. Normally, they are mounted with the thicker end at the rear. That props up the aft end of the scope.

Mounting the rail that way has the same effect as dialing in "up" adjustment on your scope's elevation knob. That extra adjustment added externally lets you get sighted in at longer ranges or keep your reticle in the center of the scope when sighted in at normal ranges or, as is sometimes the case, helps overcome alignment issues between barrel and receiver.

The amount of adjustment is given in MOA but that's just a close approximation as you may put your scope in a slightly different position on the rail than the next guy. Obviously, I hope, a 25 MOA rail gives more adjustment than a 15 MOA rail.

MOA is the abbreviation for Minute of Angle or Minute of Arc. Rounding for simplicity, a MOA is an angle that measures 1" wide at 100 yards. Since it is an angular measure, 1 MOA will be 1/2" wide at 50 yards and 2" wide at 200 yards.

So, given that, we can see that a 15 MOA rail will give you the effect of dialing up your elevation knob by 15" at 100 yards or 7.5" at 50 yards.

Again, I'm rounding for simplicity. One MOA is actually slightly larger than 1" at 100 yards.

When you run out of other things to do, you might enjoy reading through this:

https://www.rimfirecentral.com/forums...d.php?t=201168

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Last edited by Sophia; 12-29-2013 at 10:39 AM.
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Old 12-29-2013, 10:37 AM
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While I am not the OP, I must say Thank You Sophia for an incredibly good, easy to understand explanation! Thank you for taking the time to post.
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Old 12-29-2013, 11:26 AM
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Yep, excellent explanation. It doesn't give you extra adjustment, it just allows your scope to be closer to center at longer ranges. Scopes tend to be more accurate and repeatable the closer to center of their adjustment range they are. My long range precision rifle with a 20MOA mount gets the scope close to center at 700 meters but I'm using almost all the down adjustment at 100. Other than correct problems, not sure why one would want one on a .22 unless you were going to shoot 150-200 yards on a regular basis....O.L.
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Old 12-29-2013, 12:00 PM
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It does both.

Given that most scopes do zero fairly close to the center of their adjustment range, at normal ranges of 25-50 yards, you only have about half their stated adjustment range available for elevation adjustment.

A 15 or 20 MOA base does tilt the scope downward and then lets you achieve zero in the upper half of the adjustment, so it does actually give you more useable adjustment for elevation on the scope.

In "what does this mean to me?" terms, it's not uncommon for a .22 LR with a scope to zero at 100 yards and be within 7-10 MOA from the end of the adjustment range, which is not enough to be able to adjust for the election at 150-250 yards. In that case a 15, 20, 25, or 30 MOA base can give you enough usable adjustment to adjust the sight for those longer distances.
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Old 12-29-2013, 12:26 PM
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Thank you all for the input and explanations, particularly you Sophia, your explanation really helped me to visualize what the scope is doing relative to the end of the barrel. So I have a much better understanding of why the PO might have installed this particular rail. Either this is/was an issue with his scope zeroing at some distance or possibly an issue with the rifle that caused the need for the 15 MOA rail. My guess is that the PO was shooting beyond 100 yrds for what ever reason and required this rail to achieve optimum setup of the scope.

The 10/22 in question is a modified carbine model with a BC HB and stock. After purchasing the rifle I read that BC barrels may have questionable performance, however I think I got a good one as this rifle shoots very well at 50-80 yrds. I have not shot it at any other distances yet but have probably 350 rnds of 40 grn Remington bulk ammo down the pipe (man is that stuff dirty!) at 50 yrds and I am tickled by the performance of the rifle, it shoots almost as well as my Savage MKII in fact, just a whole lot faster!
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Old 12-29-2013, 01:10 PM
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Old 12-29-2013, 02:59 PM
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I really can not add any thing to the excellent expainations already, BUT...
I'll take this oppertunity to present my ideals on basic ballistics. My peeve is I think the standard graphics shown is where the line of sight is the X axis and the bullet first "goes up" and then goes down to cross the line of sight twice. while this is effective, it hides the true nature of ballistics.

I prefer to have the rifle bore being the X axis and bullets path show as just the rate of drop. now the line of sight is the angle needed to achieve the desired "zeroing" of the sights.

I find it hard to believe that for centuries now, this has been known, but it is only the "special" scope mounts that used an intital MOA setting, where the majority have the scope mounts being parrelel to the axis.

with your scope set conventionally with the "flat" base that has the centerline of the scope parrelal with the centerline of the rifle bore, you will ONLY utilize half of the "up" adjustment range. If the scope was set center of its adjustment, the point of impact would be below the point of impact by the ballistic drop.

the normal expected required adjustment for a flat mounted scope will be about 15 MOA. Given most scopes only have +/- 30 MOA, you are always approaching being out of adjstment. the 15 MOA base will allow you to be in the center of your adjsutment for normal range.

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Old 12-29-2013, 03:40 PM
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Quote:
Originally Posted by JFB View Post
I find it hard to believe that for centuries now, this has been known, but it is only the "special" scope mounts that used an intital MOA setting, where the majority have the scope mounts being parrelel to the axis.
I love my Burris Signature rings with offset inserts.
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Old 12-29-2013, 05:00 PM
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Quote:
Originally Posted by JFB View Post

I find it hard to believe that for centuries now, this has been known, but it is only the "special" scope mounts that used an intital MOA setting, where the majority have the scope mounts being parrelel to the axis.
I've always wondered about that as well.

I suppose with flat shooting cartridges and practical ranges of 500-600 yards or less, and with slower rounds like the .30-30 being used over shorter 200-300 yards ranges it's never been a problem.

But now, with people shooting .22 LR at 200-300 yard ranges just for fun, and with center fire shooters shooting well in excess of 1000 yards just for fun, it's suddenly more relevant.

And, like Sophia, I'm a big fan of the Burris Signature Zee rings. In part because I can use their insert set and get anywhere from 5 MOA to 30 MOA on the rings in 5 MOA increments.
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Old 02-25-2019, 01:45 PM
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MOA trivia

MOA Trivia (with your morning coffee.)
MOA = Minute of Angle
1 MOA at 100 yards = 1”
(Note, how is the 1” at 100 yards calculated?)
1. There are 7,200” in the diameter of a 100 yard circle. 36” x 100 yards x 2 = 7,200”
2. There are 21,600 minutes in a circle. 360 degrees x 60 minutes in a degree = 21,600 minutes.
3. Formula for circumference of a circle = Pi 3.14159 x Diameter. 7,200” x Pi = 22,619.4” in the circumference of a 100 yard circle.
4. 1 MOA circumference at 100 yards = 22,619” divided by 21,600 minutes = 1.04719” for 1 MOA.
5. 1 MOA of 1.04719” at 100 yards is rounded to 1”.
6. 1 MOA at 200 yards = 2”, at 400 yards 1 MOA = 4”, at 800 yards 1 MOA = 8”, etc.
7. 1 MOA at 50 yards = ½”, 1 MOA at 25 yards = Ό”.
The 1 MOA = 1” is an ARC measurement and not a straight line as it is a very small section, 1” of the overall circle circumference at 100 yards.
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Old 02-25-2019, 02:29 PM
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They angle the scope downward, so you have to lift the barrel higher to acquire the target. For long range, or a gun that simply shoots low... it puts the shots back into the scope's range of adjustment.

Some will cut a shim out of a soda can, and put it inside the scope rings, under the rear part of the scope. Does basically the same thing, but many think it's ghetto.

Good Luck
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Old 02-26-2019, 09:27 AM
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Ask the man what time it is and he explains how to build a clock!!! Great job!!

Quote:
Originally Posted by Travis299 View Post
MOA Trivia (with your morning coffee.)
MOA = Minute of Angle
1 MOA at 100 yards = 1”
(Note, how is the 1” at 100 yards calculated?)
1. There are 7,200” in the diameter of a 100 yard circle. 36” x 100 yards x 2 = 7,200”
2. There are 21,600 minutes in a circle. 360 degrees x 60 minutes in a degree = 21,600 minutes.
3. Formula for circumference of a circle = Pi 3.14159 x Diameter. 7,200” x Pi = 22,619.4” in the circumference of a 100 yard circle.
4. 1 MOA circumference at 100 yards = 22,619” divided by 21,600 minutes = 1.04719” for 1 MOA.
5. 1 MOA of 1.04719” at 100 yards is rounded to 1”.
6. 1 MOA at 200 yards = 2”, at 400 yards 1 MOA = 4”, at 800 yards 1 MOA = 8”, etc.
7. 1 MOA at 50 yards = ½”, 1 MOA at 25 yards = Ό”.
The 1 MOA = 1” is an ARC measurement and not a straight line as it is a very small section, 1” of the overall circle circumference at 100 yards.
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Old 02-26-2019, 12:34 PM
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MOA Rail In newbie talk.

0 MOA rail, scope line of sight same as barrel bore. Due to gravity bullets start dropping as soon as they leave the barrel. The further they go the more they drop.
That why at longer distance you adjust your scope at the top turret to raise the point of impact, hit the target.

This up adjustment on the scope actually lowers the crosshairs/ reticle , making youpoint the barrel higher.

Most scopes have a limit on how many up clicks they have. So at some point you just can’t get the point of impact high enough.

So to fix this you get a rail that is slanted , high in back low in front, or rings with inserts that do the same thing.

The problem with this is if you get to much MOA you won’t be able to go down enough to hit closer targets.
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Old 02-26-2019, 02:15 PM
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Quote:
Originally Posted by Travis299 View Post
MOA Trivia (with your morning coffee.)
MOA = Minute of Angle
...
5. 1 MOA of 1.04719” at 100 yards is rounded to 1”.
6. 1 MOA at 200 yards = 2”, at 400 yards 1 MOA = 4”, at 800 yards 1 MOA = 8”, etc.
7. 1 MOA at 50 yards = ½”, 1 MOA at 25 yards = Ό”.
The 1 MOA = 1” is an ARC measurement and not a straight line as it is a very small section, 1” of the overall circle circumference at 100 yards.
The 1 MOA = 1" @ 100 yds is indeed a gross approximation that works for small MOA and small distances (like practical shooting distances). But what is the error if we go to larger MOAs?

Let's say we have a place to shoot that's perfectly flat and there is no pull on the bullet from gravity. We set up a scope 1" above the bore center line and align it to be perfectly parallel to the bore. We fire a shot at the 100 yard bullseye and the bullet travels straight and hits 1" low. Okay, that's our starting point. Now, lets start adding MOA.

We tilt the scope down 1 MOA and fire at the bull again. The gross approximation says the bullet will hit 1" higher than the first one. A better approximation says the bullet will hit 1.0472" higher than the first one. But this is still an approximation because MOA is an arc and not a triangle. So the bullet actually reaches 1.0472" just before reaching the target. The distance from the target is 0.01667", so the bullet will actually strike slightly higher. Maybe at 1.0473" higher than the first.

Okay, now let's change the scope to an angle of 30 MOA and shoot again. This time, the gross approximation says the bullet will hit 30" higher than the first. The better approximation says the bullet will hit 31.4167" higher. But again, the bullet will actually reach this height before reaching the target. This time, the bullet will reach the 31.4167" height a full 0.5000" before reaching the target. So the bullet will actually impact the target around 31.5" higher than the first bullet.

Math + morning coffee = fun times!!!
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