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.
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.
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
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 M4carbine.net about Lt. Col. Chuck
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.
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.
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.
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!
If I zero the 6/3 at 36 yards instead of 25 meters, should this still be pretty close?
Hi Steven, thanks is for asking! That really depends on the sight radius. It will be a bigger difference on carbine it mid length sights than on rifle. That said, it’s all really a “ball park” ordeal and should be close enough for you if you used a 36 meter zero.
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: https://www.trngcmd.marines.mil/Portals/207/Docs/wtbn/MCRP%203-01A.pdf 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 »
Hey Jim, thanks for reading and commenting! I’m glad you found it useful. I actually didn’t know that the USMC had an official recommendation for this process.
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.
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 »
Hi Russel, thanks for reading. It’s interesting because the original M16 prototypes and the M16A1 all used relatively simple “set it and forget it” sight systems. You simply picked your battlesight zero (typically 300 yards) and never worried about it again. The US military, particularly the USMC, has always been influenced by competitive shooting, though. They were the ones adcocating for the adjustable elevation drum on the A2. I can’t really speak to the efficacy of the adjustable sights in combat, but I’m sure they helped a lot during qualification at ranges to 500 and beyond. As far as your… 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 »
Hi John, So this really comes down to a lot more personal preference. The “Z” notch for 20″ barrels has more do to with the drop compensation as you rotate the knob out to 400, 500, 600, etc than it does with the RIBZ settings I’m referring to. The extra clicks have to do with the ballistic curve of the bullet as it flies. Remember that each click (on a 6/3 sight) is about 1/2 MOA, and from point blank to 100 yards the bullet will arc somewhere around 3 MOA (6 clicks). Not all of that curve is useful,… 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.
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?
As you noted when using a 20″ with the 6/3 handle zero on the “Z” setting at 25M. If I have set the sight with the 8 clicks mod setup, what setting do I actually zero on for the RIBZ? The 6/3-4 or the “Z” at 25M to achieve the RIBZ? Thanks
Hi Al, you should still zero according to the technical manual. So that would be 6/3 on a carbine-length sight and the z notch with rifle length sights. Alternatively, if you’ve done the RIBZ adjustment then you can zero for 50 or 100 yards by clicking the appropriate amount below the 6/3 setting. The RIBZ adjustment doesn’t change the BDC-nature of the rear sight drum, but rather allows for more adjustment room to get down to that 50 or 100 yard zero while keeping the rest of the drum’s BDC numbers relatively in tact.
Thanks for replying. I’ve read others that said zero at 50 on the 6/3-4. Thus the confusion. You say just zero with the “Z” at 25 with the 20″ which I do understand, and then when I click down 6/3-4 will be on at 50/200 and 6/3-6 on at 100, with all other BDC correct as marked? Do I understand you correctly?
Hey Al, your perception is correct. The catch is that the BDC of the knob is really a best guess based on a military specification of velocity, sight radius, and a particular cartridge. Any deviation from that specific combination throws off the BDC. That said, it’s probably close enough.
Hey Matt, I really like the idea of the RIBZ. What I want to ask is how much does m193 differ from m855 in regards to using the elevation wheel on a 20″ A4, since the elevation wheel is calibrated for m855 and a 20″ barrel?
Hi Josh, it took me a bit to catch up to this question. I ran the numbers through a ballistic calculator assuming a M855 at 3100 FPS and a 55gr FMJ at 3173 FPS (both of which represent the velocity for 20″ barrels respectively. For trajectory, I set a 100-yard zero, and both loads look pretty much identical out to 400 yards. At 500 and beyond, the 55gr starts dropping more quickly. The M193 needs about a half MOA more elevation at 500 (1 click), and 1 MOA more at 600 (2 clicks)