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Guys,

A couple of years ago I went to the USAMU S.D.M. Instructor course. In that school I received a lot of information about different types of iron sights for the M-16 / AR-15 rifles.

Keep in mind the U.S. Military uses the metric system for measurement. Most Americans do not understand how long one meter is much less how long 300 meters are. So here is a simple range formula to convert the two units of measure.

This is very important because your BDC elevation knob is in meters on all M-16 / AR-15 rifles.

There is 91.44 meters to every 100yds. So we will work with this to help us out. We will use the value of 300 as a test distance for this simple math.

Yards to meters

300yds x .91 = Meters

Meters to yards:

300m / .91 = Yards

So I hope this helps you all out in some way.



1. Zeroing. At a given range, a rifle is zeroed when the path of the bullet and the line of sight intersect and their resulting value in any form of measurement is zero.



2. Battle Sight Zero. A battle sight zero is a zero or sight setting that allows you to aim center mass on a target from the end of your muzzle to 350m. You will always strike the target either above or below your point of aim within an acceptable zone.



a) Pre-range checks- Bullet Drop Compensator (BDC) is bottomed out and on the 300 meter setting. This is 8/3 on A2/3’s or 6/3 on A4/M4’s.

b) The small rear aperture is up and windage index lines are centered. Also the front sight post is not bent or damaged and the sight post flange is flush with the front sight housing.
c) When zeroing at 25m, the BDC is set to 8/3 + 1 for A2/3 and 6/3 + 2(Z) for A4.



d) The M4 will be the exception for zeroing. Because the barrel is shorter, the muzzle velocity is slower. The slower muzzle velocity causes the bullet to cross the line of sight at 25m with the sight with the sight set on 6/3.

e) We zero at 25m with a different sight setting than we use to qualify with. The reason for this is, that with a good 300m zero, the flight path of a bullet fired from an A2/3/4 crosses the line of sight at 32m, not 25m.

f) Elevation changes are made with the front sight post, as this is the only way the BDC will work. Each click of adjustment on the front sight post is 1 1/4 minute of angle (MOA). Each click of the rear sight is one (MOA).

g) Changes for windage are made with the windage knob. Each click will move the strike of the round ½ (MOA).

h) Obtaining a BSZ can be accomplished at any distance between 25-300 meters as long as the distance is known, and the amount above or below the line of sight the bullet needs to impact is known.

i) Though the Army uses the 25 meter range to zero, there is no substitute for firing at 300m to refine the BSZ.

3. No Wind Zero. A no wind zero is the windage setting on the rear sight that will allow you to be in the center of the target left and right in a no wind condition.

a) Most people will be at their no wind zero after they zero at 25m. However, it is a good idea to confirm this at longer range on a day when there is no wind.

b) It is important to know where no wind is on your rear sight when you have to make corrections for strong winds. If you don’t know exactly where no wind is, it will be more difficult to return to your no wind setting.

c) In order to know where you are, the shooter will mark the windage knob. This can be done with a paint pen or some other semi-permanent mark. A mark should be made on both the knob and the scale to ensure that you have an index mark to refer to.



4. Bullet Drop Compensating. The elevation wheel on any variant of the M-16 is actually a Bullet Drop Compensator. This allows the shooter to adjust the rear sight for elevation to engage targets that are farther away than 300.

a) The BDC is only usee for shots that are farther away than 300m.

b) For the BDC to work properly the rifle must be zeroed using either the 25m or 300m known distance technique.

c) The numbers on the BDC correlate to the range, in meters, that you wish to shoot. For example, the number 5 on the BDC is for shots that are 500m away.

5. Sight Manipulation. In order to accurately manipulate the rifle’s sights, you must know how many clicks there are between the meter-line marks on the BDC, and how much each click will move the strike of the bullet.

a) A minute of angle is a unit of measure that is equal to 1.0472 inches of displacement for every 100yds of distance. To find each MOA value at any range use this simple formula:

1.0472 x range distance = MOA diameter at that range

1.0472 x 200yds = 2.0944"

So 1 MOA at 200yds is 2.0944 in diameter

b) It is important that you understand how many minutes each click of the sights will move the impact of your shots, regardless of the sighting system used. Without this, you will not know how much to move your sights for shots at varying ranges.

One of the fastest ways to get good DOPE " Data On Personal Equipment" is to use a bilisitic program. I like the Sierra program myself. Here is a basic chart for Blackhills 77 SMK factory load.

A chart in meters



Same ammunition in Yards



By studying these two charts you will see the difference in MOA when you dial in meters and shoot on a yard range. Do the math, find the DOPE and have fun.

Hope this helps.

John
 

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Lots of data............ouch........brain cramp............Oh well, I've been lucky and served with foreign troops and used NATO weapons in the metric system. Gets easy when you use it every day. Liter beers, 40 ouncers. The US is the last bastian of the old English measureing system. Even Great Britain has nuckled under to metric system. We should also, IMO. Thanks for the hard work as 7.62 above said........................Mike
 

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This is some good info. The print inside the figures is hard to read. One thing that you should clarify is that the elevation AND windage adjustments for the A3 are 1/2 moa. This contradicts what the Bushmaster tech expert told me over the phone. The expert was also incorrect in explaining that the large and small apertures are same plane when in fact they are not. At 100m the large aperture will drop the group down 4 moa compared to the small aperture (in my own tests). The large aperture also pushed the group 2.5 moa to the left compared to the small aperture.
 
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One little trick I learned from an older USMC instructor was that on the A2 sight system there are 5 " clicks" on the elevation wheel over the 800 meter setting. He said quite frankly how often is one going to use these. So he showed me how to back out the allen head screw and turn the 2 piece drum so that 3 of the clicks were on the bottom. Then we zeroed at 300 meters with the drum at the 300 meter setting with a point of aim -point of impact setting. Then the rule was 2 clicks down for 200 meters and 1 more for 100 meters. Now instead of having a BZO of just 300 meters, I can fine tune when hunting/plinking etc for 100 and 200. Sure does make it nice when trying to hit a small target at 100 yds without shooting over the top.
 

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This is some good info. The print inside the figures is hard to read. One thing that you should clarify is that the elevation AND windage adjustments for the A3 are 1/2 moa. This contradicts what the Bushmaster tech expert told me over the phone. The expert was also incorrect in explaining that the large and small apertures are same plane when in fact they are not. At 100m the large aperture will drop the group down 4 moa compared to the small aperture (in my own tests). The large aperture also pushed the group 2.5 moa to the left compared to the small aperture.
.5 MOA clicks are required because the same handle is used on both the A4 and M4.

One little trick I learned from an older USMC instructor was that on the A2 sight system there are 5 " clicks" on the elevation wheel over the 800 meter setting. He said quite frankly how often is one going to use these. So he showed me how to back out the allen head screw and turn the 2 piece drum so that 3 of the clicks were on the bottom. Then we zeroed at 300 meters with the drum at the 300 meter setting with a point of aim -point of impact setting. Then the rule was 2 clicks down for 200 meters and 1 more for 100 meters. Now instead of having a BZO of just 300 meters, I can fine tune when hunting/plinking etc for 100 and 200. Sure does make it nice when trying to hit a small target at 100 yds without shooting over the top.
Marine rifles and carbines all come from the factory set to bottom out at 8/3 or 6/3. The 2111s reset the sight to bottom out at 8/3-3 or 6/3-6 in order to allow the 200 meter zero used on the KD course. I have had to reset hundreds of M4/A4 sights before because of this.
 

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aimed point !

ok great work but iron sight setting is done by 50 yds at 300 meters add one back click too if this is done at 100yds is 1.5 '' high app. so all iron sight shots will count !
 

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ok great work but iron sight setting is done by 50 yds at 300 meters add one back click too if this is done at 100yds is 1.5 '' high app. so all iron sight shots will count !
I am not really sure what you are saying? Are you talking about the IBZ done at 50 yards? That is far from the standard in either the Army or Marines. The Army generally does the 25 meter BZO with the sight either set on 6/3 or Z for the M4 and A4 respectively. The Marine generally do the 36 yard BZO with the sight set on 8/3 (or 6/3) or the 200 Zero with the sight set on 8/3(6/3) minus 2 (minus 4).
 

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Sorry for pulling an old thread back at the front. I am new to AR’s. Bought my first 2 M4 flat tops back in 2013. So for I have built 20 AR15’s in 3 different flavors, 22cal 45acp and 5.56 and 2 AR10 clones, a Carbine and a Rifle. I don’t have any military experience with the AR’s; I was in the Navy during Nam 71-75. I’ve been a M1 Garrand, M14/M1A, M1 Carbine, and Mini 14 type of guy. The only reason I bought my first AR’s was for commonalty.

This has been the best info I have found on how to adjust the sights on these things. So for I have built a couple of flat tops with the detachable A2 rear site. This info is most helpful, Thanks for the hard work you put in to it.

Wolf
 
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