M16A2 sight in process and general questions

So the 25 meter zero is for the Army and roughly correlatrs to a 300 meter zero. The USMC use a 36 yard zero which roughly correlates to a 300 yard zero.

I ran the two zeros through a ballistic calculator shooting a 55 grain bullet at 3200 FPS muzzle velocity.

The 25/300 meter zero shows a maximum height of roughly 6 inches at 200 yards. At 100 yards its 3.9 inches high.

The 36/300 yard zero showsa maximum height of roughly 4.5 inches at 175 yards. At 100 yards its 3.1 inches high.

The best for iron sights in general is either the 25M/300M zero or the 36Y/300Y zero. That is what the A2 sights are designed for and also makes best use of the elevation drum. Both work as intended. We always used the 25/300 zero when I was in the Army and issued the M16A1 and M16A2. I have since started using the 36/300 zero which to me works a little better.

With either zero, you sight the rifle in at 25 meters or 36 yards, then return the drum to 3/8. You are now good for target from 25 meters out to 300 meters without any sight adjustments or the need to use hold overs. These are known as battle sight zero's ad are good for combat use. Remember that the A2 and M4 are allowed to be up to 4 MOA at 100 meters using M855 ammunition.

Yes a 50/200 BSZ makes perfect sense when using a red dot or similar optic. But the A@ elevation drum is setup for either a 25/300 or 36/300 BSZ. Yes things will change a little since you are using 75 grain bullets. Best thing is to choose either the 25/300 or 36/300 and then see where your rifle and ammo hit at different distances.

Don't overthink things with all of the different battle sight zero's.

12Bravo20 said:

Yes things will change a little since you are using 75 grain bullets. Best thing is to choose either the 25/300 or 36/300 and then see where your rifle and ammo hit at different distances.

Don't overthink things with all of the different battle sight zero's.

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That...^^^

Because the sight graduations are not intended for 75grn bullets, you will have to work up your own sight dope based on your particular load. I would probably zero it at 25M... that would give you a good baseline for your zero, and be reasonably accurate when you adjust for elevation.

As far as accuracy potential... with a good load worked up with a good 75grn match-type bullet? I don't see why 1MOA wouldn't be workable... assuming the rifle is up to it, as well as the shooter skill.

When I started shooting and testing loads for my A4 clone I threw out the numbers on the elevation drum. That rifle has seen about one magazine of factory ammo since I got it over a year ago. Using hand loads for the rifle means I’m certainly not matching the military standard loads and drum set for them.

My drum is set for a pair of ranges. Many times I only shoot at 100 yards. For those days I ran the drum to the bottom and zeroed for 100 yards using the front sight and my standard 77 grain SMK load.

For general use I set the drum to hit 3 inches high at 150 yards. Then I loosened the set screw in the drum and turned it so the 8/3 flat facet is in the “0” position. This gives me a maximum point blank range for a 6” diameter target out to 275 yards or so. In other words farther than I can see a 6” target reliably. When I get a chance I’ll mark the drum for a 300 yard zero.

C-grunt said:

So the 25 meter zero is for the Army and roughly correlatrs to a 300 meter zero. The USMC use a 36 yard zero which roughly correlates to a 300 yard zero.

I ran the two zeros through a ballistic calculator shooting a 55 grain bullet at 3200 FPS muzzle velocity.

The 25/300 meter zero shows a maximum height of roughly 6 inches at 200 yards. At 100 yards its 3.9 inches high.

The 36/300 yard zero showsa maximum height of roughly 4.5 inches at 175 yards. At 100 yards its 3.1 inches high.

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wouldnt you need a 20" barrel to get 3200 FPS? M-4's have 14 inch barrels I think and the civilian type is 16 where you might get 3000 FPS I would think

The sight in procedure is the same for both the M16A2 and the M4. You start with a 25 meter battle sight zero with both which will get you very close at 300 meters.

Here is a photo taken from the Rifle Marksmanship M16/M4 Series Weapons FM 3-22.9 dated August 2008



https://www.benning.army.mil/infantry/DoctrineSupplement/ATP3-21.8/PDFs/fm3_22x9.pdf

jmr40 said:

I've yet to understand why anyone would think hitting 4-6" above point of aim at the ranges where you are most likely to shoot is a good idea. You're going to be high enough to miss at even 50 yards. Seems like there has to be a better way. What does the military do now that they have moved to optics?

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While the 25/300 zero might not be the best, it has worked just fine since the 1960's and serves the military just fine. I had to use the 25/300 zero while I was in the Army but prefer to use the 36/300 zero for iron sights now days. Most of my ARs with red dots are sighted in at 50 yards and I am rethinking that one too. I might relight my red dots for 36 yards also.

jmr40 said:

I've yet to understand why anyone would think hitting 4-6" above point of aim at the ranges where you are most likely to shoot is a good idea. You're going to be high enough to miss at even 50 yards. Seems like there has to be a better way. What does the military do now that they have moved to optics?

I use optics and zero at 100 yards. I'm no more than 1" above, or below, point of aim from 50-150 yards and no more than 6" low at 300. Seems to me it is a lot easier to hold over by a bit at long range than hold under at shorter ranges.​

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as far as I see it you are totally correct. 100 yd zero for the AR is just about right for 90% of shooting

jmr40 said:

I've yet to understand why anyone would think hitting 4-6" above point of aim at the ranges where you are most likely to shoot is a good idea. You're going to be high enough to miss at even 50 yards. Seems like there has to be a better way. What does the military do now that they have moved to optics?

I use optics and zero at 100 yards. I'm no more than 1" above, or below, point of aim from 50-150 yards and no more than 6" low at 300. Seems to me it is a lot easier to hold over by a bit at long range than hold under at shorter ranges.​

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Because they are trying to hit a relatively large target (torso) with the least amount of thought as far as they can.

How can you zero for both 25/300 and 36/300 with the same rifle, sights, and load?

jmr40 said:

Seems to me it is a lot easier to hold over by a bit at long range than hold under at shorter ranges.

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It's easier to aim a little low at closer ranges, than it is to hold high... and obscure the target... at longer ranges.

DMW1116 said:

How can you zero for both 25/300 and 36/300 with the same rifle, sights, and load?

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You can't . One has to choose one or the other. The Army uses the 25 meter/300 meter zero while the Marine Corp uses the 36 yard/300 yard zero. Part of that is all Army ranges are in meters while the Marine Corp left most if not all ranges set to yards. I have to say that the 36/300 zero is a little better than the 25/300 zero after using both.

Ah got it. At 50 yards mine seem dead on but that’s just an accident from the +3” @ 150 yard setting. The far zero is something like 240 yards but I’ve not tried it that far. When starting new I zeroed at 50 to be sure I was on paper. Then adjusted from there for 150.

jmr40 said:

I've yet to understand why anyone would think hitting 4-6" above point of aim at the ranges where you are most likely to shoot is a good idea. You're going to be high enough to miss at even 50 yards. Seems like there has to be a better way. What does the military do now that they have moved to optics?

I use optics and zero at 100 yards. I'm no more than 1" above, or below, point of aim from 50-150 yards and no more than 6" low at 300. Seems to me it is a lot easier to hold over by a bit at long range than hold under at shorter ranges.​

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Im not sure someone is going to be able to really hold for a 6 inch difference in POA/POI at 200 meters in a firefight.

The ACOG is zeroed for the reticle.

The red dots are usually zeroed the same as irons. A 4 MOA dot is going to cover 8 inches at 200 meters. Even a 2 MOA dot is covering 4 inches on the target. So the bullet is going to travel just above or stay inside it out to about 400 meters.

12Bravo20 said:

The sight in procedure is the same for both the M16A2 and the M4.

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No. Not quite.

With the M16A2 and M16A3, you start with the elevation knob at 8/3, plus one click.

With the M16A4, you start with the elevation knob at 6/3, plus two clicks.

With the M4/M4A1, you start with the elevation knob at 6/3.

DMW1116 said:

How can you zero for both 25/300 and 36/300 with the same rifle, sights, and load?

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The USMC (M16A2/M16A3) 36 yard zero starts with the elevation knob at 8/3, the Army's 25 meter zero is as noted above plus one click.

12Bravo20 said:

You can't . One has to choose one or the other. The Army uses the 25 meter/300 meter zero while the Marine Corp uses the 36 yard/300 yard zero. Part of that is all Army ranges are in meters while the Marine Corp left most if not all ranges set to yards. I have to say that the 36/300 zero is a little better than the 25/300 zero after using both.

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Nope. the USMC's 36 meter zero yields a 300 meter zero.

All of these will yield a 300 meter zero.

lysanderxiii said:

No. Not quite.

With the M16A2 and M16A3, you start with the elevation knob at 8/3, plus one click.

With the M16A4, you start with the elevation knob at 6/3, plus two clicks.

With the M4/M4A1, you start with the elevation knob at 6/3.

The USMC (M16A2/M16A3) 36 yard zero starts with the elevation knob at 8/3.

All of these will yield a 300 meter zero.

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When I said they are the same I was talking about the distances that you shoot at to zero each. And yes you still use the 25/300 zero no matter if you are using the A1, A2, A4 or M4.

jmr40 said:

I've yet to understand why anyone would think hitting 4-6" above point of aim at the ranges where you are most likely to shoot is a good idea. You're going to be high enough to miss at even 50 yards. Seems like there has to be a better way. What does the military do now that they have moved to optics?

I use optics and zero at 100 yards. I'm no more than 1" above, or below, point of aim from 50-150 yards and no more than 6" low at 300. Seems to me it is a lot easier to hold over by a bit at long range than hold under at shorter ranges.​

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The zeroing is done with the LONG RANGE sight (small aperture).

Once you flip to the SHORT RANGE sight (big aperture), you are now zeroed at 200 yards.

With the big aperture the only time you need to hold off is at the longer ranges if you don't want to flip the sight.

12Bravo20 said:

When I said they are the same I was talking about the distances that you shoot at to zero each. And yes you still use the 25/300 zero no matter if you are using the A1, A2, A4 or M4.

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But, the initial settings are crucial to getting the correct zero, especially when you flip to the big aperture for qualification.

I cannot say how many qualification bolos I have seen from not setting the elevation drum right when zeroing.

lysanderxiii said:

But, the initial settings are crucial to getting the correct zero, especially when you flip to the big aperture for qualification.

I cannot say how many qualification bolos I have seen from not setting the elevation drum right when zeroing.

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While this is true, the OP asked what distance to zero at, not how to set up the rear sight. And the correct answer is to use the 25m/300m or 36y/300y zero with all variants of the M16 and the M4 carbine.

JCSC said:

The milspec procedure for sighting in the 3/8 sight sure has a lot of variances when it comes to initial target distance when set at 3/8-2. I saw 25, 36 and 50 meters referenced in different articles.

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I had to use the 25m/300m zero for many many years while in the Army. I tried the 36y/300y zero and find it better with a flatter trajectory at ranges between 25 meters and 300 meters. Plus you don't have to mess with the elevation drum or flip between the small and large aperture. This makes things much simpler.

JCSC said:

I am guessing that my 100 and 200 yard shots will be 1-2-1/2” high and there is obviously no solid 100 yard setting.

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When you zero at 25 or 36 meters, you zero with the small aperture, when you flip to the large aperture the zero changes to a 200 meters.

(and, it is plus 2 clicks, not -2)

If you plan on zeroing at a reduced range (and I strongly recommend zeroing at the actual range, if possible), read FM 3-22.9, Chapter 5, Section II for the M16A2/carry handle sights and Chapter 8, for optics, either magnifying or red dot. If you want to use the 36 yard reduced range zero, read MCRP 3-10A, Chapter 8

12Bravo20 said:

While this is true, the OP asked what distance to zero at, not how to set up the rear sight. And the correct answer is to use the 25m/300m or 36y/300y zero with all variants of the M16 and the M4 carbine.

I had to use the 25m/300m zero for many many years while in the Army. I tried the 36y/300y zero and find it better with a flatter trajectory at ranges between 25 meters and 300 meters. Plus you don't have to mess with the elevation drum or flip between the small and large aperture. This makes things much simpler.

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If your weapon is zeroed to 300 meters/328 yards, the trajectory is the same. It doesn't matter if you did it at 25 meters or 36 yards.

NOW, THE ELEPHANT IN THE THREAD.

All of the military zero procedures are based on M855/M855A1 fired from a 14.5 inch barrel (2,870 fps) or a 20 inch barrel (3,100 fps). If you are planning to shoot 75 gr bullets at 2,600 fps, I strongly suggest you study the trajectory of your loading and compare it to M855 and adjust either the initial sight settings or the point of impact location relative to the point of aim, as these will be quite different from the military stuff.

lysanderxiii said:

When you zero at 25 or 36 meters, you zero with the small aperture, when you flip to the large aperture the zero changes to a 200 meters.

(and, it is plus 2 clicks, not -2)

If you plan on zeroing at a reduced range (and I strongly recommend zeroing at the actual range, if possible), read FM 3-22.9, Chapter 5, Section II for the M16A2/carry handle sights and Chapter 8, for optics, either magnifying or red dot. If you want to use the 36 yard reduced range zero, read MCRP 3-10A, Chapter 8


If your weapon is zeroed to 300 meters/328 yards, the trajectory is the same. It doesn't matter if you did it at 25 meters or 36 yards.

NOW, THE ELEPHANT IN THE THREAD.

All of the military zero procedures are based on M855/M855A1 fired from a 14.5 inch barrel (2,870 fps) or a 20 inch barrel (3,100 fps). If you are planning to shoot 75 gr bullets at 2,600 fps, I strongly suggest you study the trajectory of your loading and compare it to M855 and adjust either the initial sight settings or the point of impact location relative to the point of aim, as these will be quite different from the military stuff.

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No that is not 100% correct either. It has been proven time after time that POI changes at ranges between 25 meters and 300 meters depending on if you use a 25 meter zero, 36 yard zero, or 50 yard/50 meter zero or 100 yard zero.

Here is a good photo showing the different zeros. Granted that was with 55Gr FMJ. The red dots are the zero distance. A simple Google search will tell you this.




Now to address the ELEPHANT. I did state in my very first reply in this thread for the OP to go a head and use the sight in distance of his choice and then verify the POA/POI for his particular ammunition.

12Bravo20 said:

Yes a 50/200 BSZ makes perfect sense when using a red dot or similar optic. But the A@ elevation drum is setup for either a 25/300 or 36/300 BSZ. Yes things will change a little since you are using 75 grain bullets. Best thing is to choose either the 25/300 or 36/300 and then see where your rifle and ammo hit at different distances.

Click to expand...

12Bravo20 said:

It has been proven time after time that POI changes at ranges between 25 meters and 300 meters depending on if you use a 25 meter zero, 36 yard zero, or 50 yard/50 meter zero or 100 yard zero.

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Then the 25 meter, 36 yard, and 50 yard reduced range zeros are not actually giving you a 300 meter zeros but something close.

The definition of a 300 meter zero would be that the bullet hits the point of aim 300 meters distance from the the weapon. And, since the trajectories of bullets are solely based on their velocity, if you have a 300 yard zero, the bullets will follow the same path and have the same ordinates.

Now, if you are stating that a 36 yard reduced range zero is closer to a true 300 meter zero, that may be.

(By the way, your chart looks like you forgot to add those two clicks on your elevation knob with the 25 meter one . . .)

lysanderxiii said:

Now, if you are stating that a 36 yard reduced range zero is closer to a true 300 meter zero, that may be.

(By the way, your chart looks like you forgot to add those two clicks on your elevation knob with the 25 meter one . . .)

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Actually the person that made that chart and associated video was using a red dot sight.