An Improved Battlesight Zero for the M4 Carbine/M16A2 Rifle

Len-2A Training

NES Life Member
NES Member
Feb 26, 2005
Feedback: 75 / 1 / 0
Compliments of LTC Chuck Santose, the following website/forum has an excellent set of instructions on setting your Battlesight Zero for the M4 Carbine and AR15 A2 Rifle.

Since Microsoft has killed off MSN Groups, the link was dead.

Here's the info in a PDF that should live on NES forever.

View attachment LTC Chuck Santose ImprovedBattlesightZero.pdf
Last edited:

Thanks for posting this. I had seen this site before but never book-marked it so I kept losing it. I have a Bushmaster A3 Carbine, I wonder if I can get a new A2 carry handle and set it up to this configuaration?
Frosty - I'm no expert on the detachable carry handles but I think Ned is correct. I believe they have a slightly lower height-over-bore and may require a taller front post.
You guys are right.With Bushmaster rifles you will need the .040 higher front post to zero the detachable handle properly.Colt front sight bases marked F are not taller its just the shelf that holds the post is machined out .040 higher as it still uses a standard post.IBZ Its easy to do take a 1/16th allen wrench and flip the arperture to the small one then you will see a hole in the rear sight base..loosen the screw until the bottom of the elevation drum is movable as its a 2 part piece.Hold the upper part on 8/3 while rotating the bottom part up 2 clicks..retighten and now when the drum is on 8/3 it will already be 2 clicks higher.Now the zero is good from 50 to 200 yds perfect for a carbine.To those who dont want to fiddle around with the sight just elevate the rear drum 2 clicks.It also in my experience works at 25 yds as well.The rifle will shoot point of aim..instead of lolipopping the sight picture the rifle will shoot point of aim or impact right on top of the front poste.You could do it on a 20" rifle but its realy not necesary as the site radius is normal compared to the shorter radius of the carbine.For guys with Bushmaster flat tops dont buy the $5 part +$10 shipping call them up give them the ser# tell them your having problems properly zeroing it and they will send one free to you.They should put it on the flat tops to begin with but I think most folks who get flat tops go right to a red dot sight or other optic so it goes un noticed.For those who use a BUIS,back up iron sight get the ARMS#40 L wich is lower and can be used with a normal post and you wont need a .040 higher one.,.you will only need it if you use the carry handle irons or cut down a handle and use the rear portion as your BUIS.[smile]Also anybody whos gonna be at braintree on March18th Ill be on the range from 1 to 4 or 5 when ever dusk comes.I always have my tools with me and would be more than happy to do it for you and show you how to do it.

When a man has nothing wich he is willing to fight for,nothing he cares more for than his own personal safety is a miserable creature who will never be free....unless made and kept so by the exertions of men better than himself.
John Stuart Mill
Last edited:
Dave: I may just take you up on the offer to help me zero my BUIS.
My wife and daughter will be out of town that weekend, so I have a clear schedule.

I would like to point out that the Newer 5.56mm crosses the Line of Sight twice at 36 yds and at 300yds. The FMs say 25yds and 250yds.
I just did a Unit Qual and I argued with the MTU for 20 minutes. Their procedure was 25yds. when Zero was set take 2 clicks off. I tried telling them, even thought the Qualification was going to have 100 and 200 besides the 300, that the Group should technically get TIGHTER.
Groups were not that impressive and I am sure if they used the 36yd and 300 yd fact, they would have made DOPE adjustments from the 36yd versus the 25 yrd and had better Qualifications amongst their shooters.
I will suggest to forget the 25 yd sight in tha the FMs rave about and move it back to 36yds and you should see the difference you are seeking for a GOOD, SOLID ZERO.
Maybe I shouldn't say this, but every time I have come across this IBZ website, I try and reread it and find out why it makes more sense or is somehow better than doctrine.

I guess it is all predicated on Col. Santos's belief that a a 300m zero puts the max ordinate too high for typical combat scenarios, but I ask, what is the leaf marked 0-200 for? If he wants a 200m zero, then why not follow doctrine on zeroing and then just flip the leaf down?

Every time I read it, I scratch my head and try and figure out what exactly is it that he is trying to say. Is this just me? Is he telling us to make a better cup of joe, by adding the coffee to the boiling water instead of the water to the coffee?

Does someone that understands it explain it to me in less than 50 words?


Am I correct that simply flipping the leaf to 0-200, essentially accomplishes the same thing, albeit with a larger aperture?

In the Corps, the only time we used the large aperture was at night. It is worthless, in my opinion, for anything else.

Interesting........[thinking]. Next time I go to shoot, I'll shoot a few rapid strings with the larger aperture to see how it goes. (I might have to swap out the rear sight leaf as all of mine are NM ones).

Battle Sight Zero is a Zero that isn't really for Competition, it is to maintain the 36 inch kill zone of the enemy at all ranges that they may be encountered at.
At least that what was the intial intent of BSZ. Most Soldiers/Marines will hold a Center Mast in Combat, BSZ allows a 18" deviation and still get a KILL.
For a Precision Zero for Competition, I would personaly Bench at 36 yds, exactly at the Muzzle and sight for Center. I would then move to 300 yds, at the muzzle, bench and confirm.
Then again when I was activily shooting, I had every yard line ZERO'd and Confirmed. The dope was on the side of Rifle Stock. I only needed to adjust for Light Conditions, Whether etc.
I found that back to the 400 yard line, I only had to Flip the LR Sight and was good to go. Depending on Barometric Pressure, I may need to add 1 or 2 clicks, but not often.
I was in the grunts, so I do understand what the BSZ is for and its application. My confusion comes from the wordy description for basically (as far as I can understand it) zeroing the small aperture for 200m. Part of that confusion stems from the fact that the article really is lacking a good explanation for why the already provided 0-200 aperture is inadequate for its purpose. TonyD seems to think that it is only good for low light, but I'm going to test it to see how I can shoot with it. I never got a chance to use it when I was in the service as I shot with a 300m zero like I was told.

Brian - I think there is a difference between the Corps and the Army as to aperture. If I'm not mistaken, the Army does teach flipping the rear site aperture for distance. The Corps does not. The larger the aperture is the harder it is to maintain site alignment. Site alignment is more important than aiming point.

The center axis above the bore of the larger aperture is different than center axis of the smaller aperture. The problem is trying to align the same size front site post in a bigger window. Thus we only used it in low light because the bigger the aperture the more light it let in.

You also have to take into account that Marines start their shooting at 200 yards and progress farther. So there is no practical need for anything less.
Brian, the IBZ starts to make more sense when you realize that the primary sight of the overwhelming majority of US infantry weapons is an Aimpoint or EOTech 1X optical gunsight where elevation adjustments are impossible to do in the heat of the moment and have no stadia for elevation compensation in their reticles (dot or dot inside a circle, respectively).

Then add that most infantry engagements happen inside of 250 yards and the Santose IBZ makes eminent sense.

I have my carbine set up that way and hits to 300 yards are very easy. Run any ballistics program to see, but with M193 ammo, my carbine shoots within 1.5" (roughly) of point of aim from 50 to about 225 yards and about 6" low at 300. If I needed to hit something at 300, aim for the shoulder line and I will hit COM.
Actually, the Large aperture is for night and Tony is 100% correct. but and now try and follow me. There is a SWEET SPOT inside BOTH apertures. If you look carefully at the little sight there is a real small pinpoint of clear area, if you set that sweet spot on the front sight, the front sight will become crystal clear, with little or no concentration from YOU the shooter. Now look at the Larger aperture and you will notice that the aperture itself is NOT Centered and is actually off centered just a whisker. It too has a sweet spot and by using the Long Range / Low Light your Elevation will be affected by two clicks. Now for you EXPERIENCED shooters, you should already know about the Sweet spot, but if not, hold the muzzle down towards the ground and then hold your head about two feet from the sight until you can see it, now as you bring your eye to the spot you shoot from, hopefully with your Nose smashed against the Charging Handle, you will see the spot and you only have to put it on the front sight and follow your other procedures from there.
We flipped the RS to LR/LL only if we were having to do a quick change, Rattle Battle, Sun went behind a cloud etc and mostly ONLY on the older A1s, for changing Elevation was ONLY on the Front sight with a Nail and there was no means to adjust elevation from the rear. With the A2s it is now up to the disgression of the shooter whether they Flip or Adjust, I never used it after we got rid of the M16A1s and went with at least A2 Uppers.
But the LR/LL is a 2 click change, for most shooters, regardless.
Last edited:
Then add that most infantry engagements happen inside of 250 yards and the Santose IBZ makes eminent sense.

Yeah, I do agree.

I had no problem hitting with the A1 or A2 when we went to qualify, but if I remember I did favor a little low on some of the targets in the middle. With the A2 we did shoot the course of fire with the small aperture as that is what we had been told to to do. I guess I just assumed that the large aperture would work fine for what I thought it was designed for. I'm still going to try it to see if there is any appreciable difference in accuracy. It was a long time ago that I was in, but I think I remember them telling us to use the 0-200 in close engagements and low light.

Tony, I agree that the larger aperture is more difficult to align, as you really are looking through a basketball hoop. When it warms up I'll try it with M855 and some of my handloads just to see how the two group out of the rifle with the large and small aperture. [smile]

Tony, I agree that the larger aperture is more difficult to align, as you really are looking through a basketball hoop. When it warms up I'll try it with M855 and some of my handloads just to see how the two group out of the rifle with the large and small aperture. [smile]


Let me know what you come up with. As WingWiper pointed out, a 300 yard BZO will allow a 7 MOA drop (average) at 500 yards. Aiming center mass you might get lucking and hit the enemy in the ankle, probably not.

Like Jose pointed out, most engagements occur out to 250 yards. Using the IBZO you have a six to nine inch MPBR out to 300 yards. It just gives you a much greater kill potential throughout the most common ranges of engagement.

If you need to hit something out to 500 - 600, well, that's what knowing your dope is for. However, the biggest challenge is range estimation.
I always assumed that the 0-200 was good to go with for shorter range engagements I found this in the TM 9-1005-319-10. Like I said though, I don't know how I'll shoot with the larger aperture. Assuming I do well with it, it doesn't mean that the average Soldier or Marine would do well with it either, but it should be interesting.

The Corps does not follow the same mantra as the rest of the militry in regards to firearms training.

As far as CQB goes, I only use the front sight post.

If you're in a firefight, engaging the enemy at all different ranges, you're not going to be flipping the rear sight up and down - that's what the BZO is for.

A lot of this is becoming moot with more M4's and CQB optics.

Don't forget that FMs and TMs are not written with Precision Competition in mind, but rather with being able to stay within the KILL Zone.
Tony is correct with his assertion that you don't have time to play with flipping sights etc. 95% of the Army and I would say a hefty number of Marines, once they leave the 2 week Rifle Course, are never going to be challenegd in executing the knowledge they learned about Shooting, other than Point and Aim. TMs and FMs are written for them and not for the advanced shooter who wants to be much more precise. That is what is controlled by Matches and the Marksmanship Training Units. It ends up being a small number who will become better than an average shooter for that Branch of Service..
Over all BPM, if it works for you, great. I would also suggest to stay with the smaller Aperture. There is really no need with the A2s to have to use the Larger Aperture. AS I had written about the A1s in my earlier post, YES. when you needed a 2 click change quickly and there was NO time to get a nail and adjust the front sight post. A2s have the ability to adjust Elevation in the rear.
Last edited:
I set up my carry handle sights for an Improved Battlesight Zero last night and am off to Harvard today to sight-in on the 50. I ran across this shot trajectory table that was helpful to me in understanding the different zero distances. Thought others might find it useful too.

according to bushmaster if you are using an ARMS inc #40 Back Up Iron sight you need the taller front sight post. I checked there online catolg and it staes the same in the sight section.
The Bushmaster carry handle worked with the front post that came on my Stag upper. Worked like a charm at the 50, but when I moved to the 100 shots were way more than 1.5" high. More like 5". Not sure what the deal was. I was shooting handloads that are not that hot. Anyway, Im off to Braintree tomorrow to shoot a 100 yard CMP match. Hopefully a 6 o'clock hold on the 6" targets will be in the ballpark.
Please see Top Post here.

Since all MSN Groups "went South", the original link was dead and most Google references are too! [sad]

With many thanks to "11Bravo" on who saved it to a PDF before the MSN Groups disappeared . . . I have attached the PDF to the Top Post here.
I realize this post is really old, but I figured it could use an updated opinion anyway (hopefully it is welcome and not shunned, as I'm green as the grass so far as being a member here is concerned.)

Background: New Corps Marine...trained on M16a4's with iron sights on Parris Island. These rifles are extraordinarily similar to those being sold on the civilian market (in every state but CT, where my current reserve unit is).

Our BZO was always done at 36 meters (equivalent to 300 meters on the other side of the projectiles trajectory for M855 62 Grain green tip NATO ammo) and have qualified in shooting at targets from 20 meters in table 2, to 500 meters in table 1 all using the aforementioned 'peep' or small sight aperture.

I guess it might be a stubbornness to stray from the method I had DRILLED into my head, but I see no reason to switch to a 200 (50) meter BZO when all targets engaged have been successfully destroyed and/or incapacitated (depending on course of action and whether target was needed for questioning or was disposable.)

So, how do we know what is ACTUALLY more effective in battle? The Devil Dogs (and the French soldiers whom accompanied them) at Belleau Wood or even the mountains of Afghanistan might have a completely different answer than those Marines fighting house to house, street to street at Khe San or Fallujah.

I trust my training, and although I have fooled around with BZO's for the backyard range (100 yards) on my personal Stag Knights Armament M16A4 service rifle stays at 36 yards and has been tested to 500 with stellar results (last qual I hit 19 out of 20 shots at the 500 on the B-mod or BODY mod target).
Top Bottom