September 15, 2020
Posted By Jason

Hi, Jason McHann here with Mountain Tactical. I thought I'd take a moment and address the most common question we receive. That is, do I get a Zero MOA optic mount or a 20 MOA optic mount? In order to explain why we make the suggestions that we make, I thought I'd take a minute to explain what Minute of Angle is, how it affects the rifle system, and why you want to choose one over the other. Let's dive into this. Alright, so what is MOA? MOA is an angular unit of measurement. Many times when somebody asks which rail they want to go with, actually they were referring to the height and what we're actually referring to is the built in cant that we cut into the rail.

Where does MOA come from? [00:01:00] MOA comes from actually the compass roads. It's been used to circumnavigate the world for as long as we've had compass roads. Remember High School geometry, there's 360° in a circle. Now, 360° could be broken down into little bits. 1° has 60 minutes of angle to it. One minute of angle has 60 seconds to it, and then you break that down into further decimal points as well. The very exaggerated blue line here, 20 MOA is a very, very thin sliver of the circle here. How does that relate to a linear unit of measurement? One minute of angle at 100 yards is roughly 1.047”, 200 yards double that, 300 yards triple that. You can see, as we extend out from this circle, that linear gap becomes larger. [00:02:00] 

Let's dive in to how this relates to the optic on your rifle. All right, we're not circumnavigating the globe. Let's see how this actually applies to our firearm. Zero MOA rails or Zero MOA optic mounts have been the way we've mounted modern optics to the modern rifle since the modern optic and the modern rifle. What you have here is you have your line of sight. All we're doing with the rail is we're manipulating the line of sight. 

Zero MOA optic mount or a 20 MOA optic mount?

With the Zero MOA rail, your line of sight is parallel to the bore of your rifle. That's the way it's been done forever. You’ve kind of asked yourself, why do we need 20, 30, 40 MOA mounts when this is worth for so long? Let's take a look at that. All right, as I said earlier, we're using the optic mount to manipulate the barrel site relationship [00:03:00] and with a 20 MOA rail, and this is a little exaggerated guys so don't think we're going to be driving your scope into your barrel, but with a 20 MOA rail, your line of sight is now downward compared to the bore.

20 minutes of angle equals one third of a degree or .33 repeating degrees. What we're doing is we're gaining unused MOA in your scope. As you can see here, whether you get a Zero or 20 MOA rail has nothing to do with your rifle. Your rifle is static. What it has to do with is your optic. Let's dive into what's happening inside your optic as we're manipulating this bore sight relationship. All right, so we've established that whether you go Zero or 20 MOA [00:04:00] is a function of your optic. 

Let's take a look at a couple of different optics and see when a Zero MOA rail would be appropriate and when a 20 MOA rail would be appropriate. First off, let's say you just have a one inch two standard duplex reticle. Something that you would typically see in like _____00:04:22 Barry-X2 or something like that. Typically those scopes have roughly 40 minutes of angle of internal elevation adjustment. What this means is that when your scope is zeroed at 100 or 200 yards, you're going to be right in the middle of that adjustment. It's important to understand that your reticle floats on a turret, or there's a couple different mechanisms that scopes use, but essentially, your reticle is floating inside your optic and can be adjusted left/right for windage, up/down for elevation. When you're zeroed [00:05:00] you're approximately dead center of this mechanism depending on your scope. You would have 20 minutes of angle of upwards elevation adjustment, 20 MOA of downward elevation adjustment. 

Now, it's important to note that the final 10% of any skill is the least reliable part of the adjustment in any turret. If you put a 20 minute of angle rail on here, you're going to use up all your adjustment area and you may not get a zero at 100/200 yards. You might have to zero it 300, 400, or 500 yards. This is a situation where we would actually recommend a zero MOA rail instead of the 20 MOA rail because you just will not be able to get a reliable zero. The general rule of thumb is if you have 15 minutes of angle or less, then you want to go with the zero MOA rail [00:06:00] at 50 minutes of angle or more or 51 minutes of angle or more go with the 20 MOA rail, so that way you're not bumping into this unreliable section of your optic mount. 

Let's take a look at when a 20 MOA rail would be appropriate. Alright, so let's take a look at an optic that has 60 minutes of angle inside of it. Now, if you're zeroed at 100 or 200 yards, and I use that interchangeably because the zero is pretty much the same. Your reticle, your target, you're going to be hitting right there. You're going to have roughly 30 minutes of angle up, 30 minutes of angle down. I don't know about you, but I've never dialed for a close-up shot. I'm always dialing for a long-range shot. On this particular optic, if I put a 20 minute of angle rail underneath it [00:07:00] and I change nothing else all of a sudden, I'm going to be 20 MOA high downrange, which is going to equate to about 20 inches at 100 yards or 40 inches at 200 yards.

I'm going to have to dial my turret back down to get my zero. Now, when I do that, that means instead of having 30 up and 30 down, I now have 10 down and 50 up. I'm utilizing MOA in my reticle that otherwise was being wasted. Let's look at a modern centerfire cartridge and see how a 20 MOA rail will actually affect that. Let's take a look at the 6.5 creedmoor. Now, Hornady just launched their 143 gr ELD-X ammo, which is pretty impressive.

ELD-X is actually long-range hunting ammo. They say, on the box that it’ll go 2700 feet per second. Now, how does that equate to everything we're talking about here? Well, if you're zero MOA and you have 30 minutes of angle worth of adjustment as we looked at on our 60 MOA scope, you only actually have 30 MOA to play with; that we’ll call it out handy dandy ballistic calculator, that'll get you to 950 yards. [00:09:00]

Obviously at sea level, so depending on where you're at that could change. Now, what happens if we add 20 minutes of angle to this and we could actually go to 50 MOA? It's more than 1200, it’s 1310 yards. That is a massive improvement over a zero MOA rail. Would I ever take a shot hunting at 1310? Absolutely not, but it's still fun target shooting. This ammo is not that expensive. So, you can go out, do some long range shooting; take your rifle, go out shoot a long-range competition and confidently be able to dial to the ranges that would exist [00:10:00] in that type of environment. 

If you have any questions, as always, contact us at the shop. 

Happy shooting everybody!