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When I attended an Appleseed shoot back in 2014, I was frustrated with the whole zeroing process. It wasn’t anything Appleseed did, but more the settings of the standard 6/3 carry handle sight I was using at the time.

You see, I was accustomed to practicing iron sight shooting at 100 meters and the Appleseed event took place at 25 meters. The 6/3 sight was never designed to easily accommodate both settings.

You could either zero it at 25 as intended, and use the elevation markings, or set it for 100 meters and not use the elevation wheel.

The RIBZ sight setting, short for Revised Improved Battlesight Zero, helps with that.

The Carry Handle

You’re supposed to zero the 6/3 carry handle at 300 meters. That also happens to correspond to around 36 meters. This works since the intersection of the sight line and bullet trajectory at 36 meters is below the bullet’s maximum ordinate. The trajectory of the bullet will continue to rise, and then begin to fall.

It intersects the sight line again around 300 meters.

M855 25 meter zero trajectory out of a 20
This chart, courtesy of Molon shows the trajectory of an M855 bullet fired from a 20″ AR-15. Notice how the bullet intersects the line of sight twice: once at 25 meters and again at 350 meters. This is the 25/300 variation.
This is all explained in great detail by the great Molon in a thread over at

Military practice is zeroing the 6/3 sight for 300 meters. Since that is significantly below a 100-meter point of impact (POI), the elevation drum bottoms out well before you can raise the POI high enough.

The military intended for all personnel to use the 36m/300m zero and then swap to the larger 0-2 aperture for fighting. The underlying concept here is called the Point Blank Zero.

The Zeroing Problem

The standard 0-2 aperture is on a different plane than the smaller unmarked sight. Specifically, it’s 2.5 MOA lower. When the unmarked sight is set for 300 meters, the larger aperture works out to about a 200-meter zero. This gives a usable battlesight zero (BZO) from 0 to 200 meters, hence 0-2.

Related Content
In addition to this article, you might want to take a look at my Complete Guide to Your Iron Sight Zero. In that article, I go into depth with how the angles and calculations work for iron sights. It provides a lot of context to this article.

The large aperture works great for fast-paced run and gun where tight accuracy standards are not required. However, it’s not ideal for marksmanship practice where precision is the priority, it’s just to large.

The best accuracy comes from allowing you to use the small aperture at a closer range than 300. Let’s make that adjustment.

Revised Improved Battlesight Zero (RIBZ)

In 2010 when I first got into ARs, I read a thread on about Lt. Col. Chuck Santose’s improved battlesight zero. Unfortunately, the original links in the thread have all expired.

The takeaway was that a 50-meter zero was a good all-around setting for backup iron sights on the AR-15 platform. Kyle Lamb said the same in his excellent book, Green Eyes Black Rifles, which I purchased while planning my first build.

I did not have a carry handle sight to worry about at the time. I was sure I was always going to use flip up sights paired with optics. Because of that, I never paid attention to the carry handle IBZ procedure. I simply set my backup sights to 50 meters and forgot about them.

Until my frustration at the Appleseed event.

The RIBZ sight setting takes the Santose IBZ one step further to achieve a 100-meter setting. The beauty of it is that you can still take advantage of a 50-meter setting as well.

All it takes is adjusting the rear sight drum.

Adjusting the Drum

To implement the RIBZ sight setting, you need to allow the elevation drum six more clicks below the 6/3 setting.

For an 8/3 rear sight, found on the A2 drum, you only need three clicks. The A2 drum has one minute of angle (MOA) adjustments, while the 6/3 has half MOA.

Molon recommends adding one extra MOA of buffer space to prevent the rear sight housing from making contact with the frame. That means one additional click on 8/3 sights and two extra clicks on 6/3 sights. This allows you to get a more repeatable zero.

Locate the Set Screw

Set the sight to the bottom setting, which should be 6/3 for detachable sights. Looking down from above, you’ll find a witness hole with a screw at the bottom.

Setting up for a RIBZ sight setting
Looking down from above with the carry handle on its bottom setting. You can see through the witness hole and find the set screw.

To slip the drum, insert a 1/16 Allen key and loosen the screw.

Do Not remove it.

Loosen it enough that you can rotate the knurled bottom part of the drum. Done correctly, you can rotate this piece individually from the numbered portion.

While keeping the Allen key and the top half of the drum in place, rotate the bottom half clockwise for eight clicks. If using the A2 8/3 drum, only go four clicks. Once the drum is slipped, retighten the set screw.

Job Done

RIBZ battlesight zero complete

You can now turn the rear drum eight clicks below the official bottom setting of the 6/3 sight.

Turning two clicks back up, so it’s 6/3 minus six, is the new 100-meter setting. Two more clicks up, 6/3 minus four, is 50 meters. The 25-meter zero remains at the 6/3 marking.

Now you have settings for 100 and 50/200 meters. The markings on the drum for 300, 400, 500, and 600 meters remain accurate.

The Front Sight

This procedure does require resetting the front sight post to the correct height. Since the entire rear sight assembly has been raised by several MOA, the front needs to be matched.

Note: The above description of zeroing at 25 meters using the 6/3 sight assumes a carbine length sight radius and barrel. If using the RIBZ on a full-size rifle, as I do, then click two notches up to the “Z” setting for your 25- meter zero, and then continue using the 300, 50/200, and 100-meter settings as normal.

Wrapping Up

I hope you found this useful. I came across several rifles in military armories that had this process performed on them. Frankly, I think it should be part of the technical manuals.

After completing RIBZ, you can keep your elevation drum accurate and use it for 50, 100, 200(ish), 300, 400, 500, and 600 meters. Good luck!



Matt is the primary author and owner of The Everyday Marksman. He's a former military officer turned professional tech sector trainer. He's a lifelong learner, passionate outdoorsman, and steadfast supporter of firearms culture.


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Oldest First
Newest First

If I zero the 6/3 at 36 yards instead of 25 meters, should this still be pretty close?


Thanks for this article Matt. The mechanical adjustment to the rear elevation drum is referenced in the Marine Corps publication Rifle Marksmanship MCRP 3-01A which I was able to download for free at the following web site: On page 9-4 in paragraph 9005 it makes a reference that the rear elevation drum needs to move 3 clicks below 8/3 and if it bottoms out at 8/3 to take the rifle to a qualified armorer for adjustment. The pub does not explain how to release the drum with a 1/16 Allen wrench and make the adjustment. I suspect that most… Read more »


Excellent. Exactly what the shooting public needs. Unless you were in The Corps would you know that all iron sights are ZEROED or bottomed out at 300 meters. So in order to get that bullseye at 100 yards you will need to make an adjustment to the rear iron sight, particularly the DRUM. Otherwise the choice is dropping your point of aim. And one other point to add that one full turn puts you on bullseye at 600 yards with a A4/M4 6/3 drumor 800 yards with a A2 8/3 drum.

Russell Moss
Russell Moss

The devils IS definitely in the details here! Why would Uncle Sugar mil-spec a less than “best practice” of mechanically zeroing a military weapon that was used in so many instances?! Did anybody bother to tell Armalite/Colt/etc that “Oh yeah” there’s this little thing you have to do to make it work and hold a zero while the enemy was blistering you with Kalashnikov’s that don’t have the same funky handle iron sights!! And unlike the gentleman in the comments ahead of me, at least he had EXPERIENCE with the 6/3, 8/3 drum. He knew it wasn’t straight forward from… Read more »


My confusion lies in the last extra 2 clicks I’m using an A4 20” AR15. So if I slip the elevation ring 8 clicks clockwise then 2 clicks back (buffer zone) and now I’m at 6/3-6=100 yds yes I shoot yds and 2 more clicks back is 6/3-4=50 yds and 2 clicks back from that is 6/3-2=? and 2 clicks back is 6/3-0=25/300 yds but we go 2 more clicks back to Z for zeroing (why not forget the Z and zero on 6/3?) why not go back 6 clicks (Buffer zone?) back 2 6/3-4=100 back 2 6/3-2=50 and 6/3=25/300?… Read more »


I resisted for too long owning an AR – mainly due to the fact that I hunt and the 223 round doesn’t match up well with the types of game I hunt. Finally broke down and bought one after seeing how much fun I was missing out on! Just got back from the range where I attempted to dial in a new AR15A2 20″ rifle with dismal results. Problem is I used an M16A1 in Marine boot and didn’t do my homework on the A2 rear sight. My MOS wasn’t infantry so I didn’t get to handle the newly issued… Read more »


A double question about the initial bottom wheel turning : when I first unlocked the wheel on my M4, I rotated it without paying much attention, and since I can’t be sure of the number of clicks I gave in a way or another.
1) Is that bad doc ?
2) How can I “reset” it if it is needed.
Thank a lot for this article.

Mick Kelly
Mick Kelly

I tend to use 75gr & 77gr bullets; my theory is that if I give myself 6 extra clicks, (instead of 8) I can still cover a 200 yard setting and if I want to shoot at 100 yards, (rarely) I can always use the 0-2 ring giving me another 2.5 MoA. This will than (should) give me an extra 1 MoA to play with at 600…does this sound correct?

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