Basic Rifle Marksmanship (BRM) Series- How To Zero Your AR15

Basic Rifle Marksmanship (BRM) Series- How To Zero Your AR15

8/3, 6/3, cats crawling up trees, 5×5=25…

Easy there Tommy, it’s not as complicated as it seems. Of course this is zeroing your AR15 and you can make it as complicated as possible but that is up to you. Or, you can take a breath and read on and take the complication out of this process.

First step, clear your rifle and ensure it’s empty, clear and safe.

Tools you will need (any one of these will do):

– A small punch, a .223/5.56 bullet or a front sight tool.

We will now set the “Mechanical Zero”

Front Sight Post
Take your tool of choice from above and adjust your front sight so the base of the front sight post is flush with the shelf of the Front Sight Block. Usually they come flushed out but if it didn’t, get to spinning. Front sight is done for now.

Rear Elevation Drum
Now the rear sight elevation is it 8/3 or 6/3 and what the hell does that mean?

Easy Tommy, this is easy.

8/3 stands for 800m/300m. Think of it as 8(00)/3(00).

6/3 stands for 600m/300m or 6(00)/3(00).

You will also see numbers 4, 5, 6 and 7 on an 8/3 and 4 and 5 on a 6/3 etched into the drum. These also correspond to their theoretical distance in meters when set at these marks.

But luckily that doesn’t matter right now. Simply spin it counter-clockwise until it is all the way down at the bottom and the flat of the 8/3 or 6/3 is lined up parallel with the Rear Sight Base. You will know because at the top of that elevation drum is an index line, it will be lined up with the index line etched underneath the Rear Sight Base. Done with the elevation drum for a minute.

Windage
Last up is the windage. Start by spinning it all the way to one side, does not matter which, just pick one and max it out. Once maxed out on your windage you will now spin it back to the opposite side counting each click until you hit the other side. Take that number and divide it by 2 and you’ll have the actual center of your windage. It’ll be somewhere around 80 clicks total. Mine range between 78 clicks to 88 clicks. Also understand that this is a “Mechanical Zero” and only means it’ll get you on paper at 25m/36y though it’s pretty close to good. As an example, my LMT A4 rear sight is 78 clicks with a “MZ” of 39 clicks. The actual zero is 43 clicks from right, plus 4 from MZ. My DPMS has 81 clicks and actual zero is at 42 clicks, pretty dang close.

A note here, if you find that you are having to make extreme windage adjustments to zero or even come close to zeroing your AR you may have a canted front sight. You’ll need to either replace your barrel or have the factory do it.

Now that your AR15 is set for a “Mechanical Zero” and you have some basic knowledge on MOA and the adjustments on your AR15’s sights it’s time to pick your distance.

You figured out which zero you wanted right? 25/300m? 36/300y? 50/200y?

How about this, we’ll do them all.

And because people get confused between the Army’s 25/300m zero, the Marine 36/300 yards zero and how to accomplish this… I am going to let you in on a little secret, but first.

The Army’s 25/300m zero
The Army has some very nice targets that tell you all the adjustments you will have to make to get you zeroed.

To start:

Set your M16/M4 target up at 25 meters (82’). If you are shooting an A2 adjust your rear elevation 8/3 drum up 1 click. If you are shooting an A4, adjust your rear elevation 6/3 drum up 2 clicks to the “Z” setting. If you are shooting an M4 leave your rear elevation 6/3 drum bottomed out flush on the 6/3(00) setting aligning the corresponding index marks on the elevation drum and the line etched under the rear sight base.

From a solid, supported prone, fire your 3 shot group and follow the instructions presented here. Once you are zeroed make sure you return your Rear Elevation Drum back to the 8/3(00) or 6/3(00) setting. You will now be zeroed at 300m, in theory, that is.

The Marine 36/300y zero
Ready for that little secret I mentioned earlier?

DO NOT ADJUST YOUR REAR ELEVATION DRUM.

That’s it. Leave it bottomed out flush on the 8/3(00) or the 6/3(00) setting aligning the corresponding index marks on the elevation drum and the line etched under the rear sight base. Set your target up at 36 yards and repeat the above steps.

That it! That is the main difference so please don’t confuse yourself with the distances between the Army’s 25m zero and the Marine 36 yard zero. It’s all in the initial setting on the rear elevation drum.

– 25m, adjust per A2 8/3 (1 click up)/A4 6/3 (2 clicks up “Z”)/M4 6/3 (no clicks up- Leave it bottomed out flush on the 6/3(00) setting aligning the corresponding index marks on the elevation drum and the receiver) settings.

– 36 yards, No clicks up- Leave it bottomed out flush on the 8/3(00) or the 6/3(00) setting aligning the corresponding index marks on the elevation drum and the receiver.

Regardless of your initial zero, the only way to know if you are zeroed at 300m/300y is to shoot at those distances.

You’ll notice I didn’t go over the 50/200 yard zero. Treat it the same way as the 36/300y zero. The main difference in the zeroing process is that I start at 25 yards. After obtaining the initial 25 yard zero I then move back to 50 yards to make my final adjustments.

6 thoughts on “Basic Rifle Marksmanship (BRM) Series- How To Zero Your AR15

  1. Is 25 clicks left of mechanical zero too excessive? I have 15 clicks until I reach the left edge with my LMT chopped handle.

    1. That is fairly excessive. You probably have an underlying issue BUT if you got it zeroed and you are happy with it and it doesn’t bother you. Then don’t worry about it. My brother had an AR that was maxed out and still 3 or 6″ left at 25 yards (this was 8 years ago)… so in his case, yeah, we sent it back to be fixed. In your case I would simply make note of it and carry on.

      1. Upon closer examination, I have a 1+ degree cant to the FSB. I’ll have to check how the barrel is indexed and maybe drill out the taper pins.

          1. Re indexed the barrel…had to shave off part of the slot for the barrel pin in receiver extension and shim it with aluminum, but it zeroes at mechanical zero now. Took a while to get out to the range, but it’s dead on now.

Leave a Reply

Your email address will not be published. Required fields are marked *