AR-15 A1 Battle Sight Zero

[Aguila Blanca]

I don't have time for a lot of trial-and-error, that's why I need to get as good a handle on this as possible before I head to the range. As I posted above, I'm completely dependent on a friend to get me onto his club's outdoor range. His time is extremely limited. We're talking about trying to get there next Saturday -- but he's not able to meet me until 5:00, which will get us to the range between 5:30 and 6:00 p.m. And the range is in a hollow behind a mountain, so it'll be too dark to see the targets well by about 7:00 or 7:30.

I envy those of you who can shoot multiple times in a week, or get to a rifle range any time you want. It must be nice, but you shouldn't assume that everyone is able to do that.

 

[raimius]

Alternative option. Get the zero with the aperture you will use the most and call it good...
Particularly if you don't shoot past the far zero of that one very often.

 

[44 AMP]

I don't have an 'L' marked on either peep. Is the 'L' aperture up when the sight is flipped forward, or when it's flipped back?

On the M16A1 sight the "L"(long range) sight is the rear one. SO, when the L is up, the other sight is down, to the front (muzzle)

When the short range is up the long range sight is down, pointed to the rear (at you, the shooter).

If your sight isn't clearly marked, its not GI spec in all ways, so there's no telling exactly what you have, other than by shooting, sorry.

The M16A1 GI 25m zero was used with the M193 ammo (55gr FMJ), there was no other at the time. What they told us was that proper zero at 25m would put us on at 250m. But then, they told us a LOT of things.

Not sure how much effect your shorter barrel will have. Obviously the shorter barrel will have less velocity than the 20" standard. If you know how much less, you can calculate the difference in trajectory.

Don't know off the top of my head about the .22s but with .30cal 100fps less velocity = about 1/2" more drop per hundred yards with the same bullet.

 

[Charlie98]

I don't have time for a lot of trial-and-error, that's why I need to get as good a handle on this as possible before I head to the range. As I posted above, I'm completely dependent on a friend to get me onto his club's outdoor range. His time is extremely limited. We're talking about trying to get there next Saturday -- but he's not able to meet me until 5:00, which will get us to the range between 5:30 and 6:00 p.m. And the range is in a hollow behind a mountain, so it'll be too dark to see the targets well by about 7:00 or 7:30.

I kind of think you are overthinking this. I would just zero it at the indoor 25yd range you have with whichever aperture you wish to use. In the real world, that sight setting will get you within 3-4" vertically at 200-300yds with M193 ammo.

 

[pblanc]

If you take a caliper and measure the height of the individual peeps above the rear sight base, one should be a bit taller than the other and that will be the "L" sight whether or not it is marked as such. I will bet that it will be the one that points toward you when the sight is flipped back and the one that stands up when the sight is flipped forward.

The M16 A1 with a 20 inch barrel firing M193 when zeroed for a 250 yard BSZ will typically shoot about 1" below POA at 25 yards using the same peep. The actual near zero using the same peep will be closer to 45 yards. The "L" peep aperture being slightly higher, will shift your point of impact up about an inch at 25 yards compared to the other peep. This allows the rifle to be rough zeroed at 25 yards, after which switching to the shorter peep should put you close to a 250 yard zero.

Of course, things will be slightly different for the 16 inch barrel. You will probably lose about 120 fps in muzzle velocity from the 20" barrel, but the near zero (approx 45 yards) and far zero (approx 250 yards) will still be close with the shorter peep. Maximum ordinate should be in the 150-155 yard range, and you will have about 2 3/4 - 3" of rise above POA at that point. So using the short distance peep you should hit within + or - 3" all the way from point blank range out to around 290 yards or so. Assuming your rear sight heights correspond to mil-spec standards, of course.

If you zero at 25 yards and use the same peep aperture for shooting at distance, your far zero is going to be much farther out (375 yards or more). Your max Y will be out past 200 yards and your rise above POA at max Y will be 10 1/2 - 11".

If you aren't sure about your rear sight specs and just want to zero and shoot using the same peep aperture, either zero to hit 1" below point of aim at 25 yards for a 45/250 yard zero. Or zero POI = POA at 50 yards which should give you a far zero of about 225 yards, and a POI within about 1 1/2" + or - of POA from 20 yards out to around 250 yards.

 

[Aguila Blanca]

Of course, things will be slightly different for the 16 inch barrel. You will probably lose about 120 fps in muzzle velocity from the 20" barrel, but the near zero (approx 45 yards) and far zero (approx 250 yards) will still be close with the shorter peep. Maximum ordinate should be in the 150-155 yard range, and you will have about 2 3/4 - 3" of rise above POA at that point. So using the short distance peep you should hit within + or - 3" all the way from point blank range out to around 290 yards or so. Assuming your rear sight heights correspond to mil-spec standards, of course.

I probably am overthinking it -- it's a failing of mine. At 75 years of age, I doubt I'll be able to train myself out of it this lifetime.

I found this article on velocity vs. barrel length. But it doesn't go down to 16" and, curiously, from 17" to 16.5" they actually got an increase rather than a decrease.

https://rifleshooter.com/2014/04/22...gth-a-man-his-chop-box-and-his-friends-rifle/

I had previously looked at Ballistics by the Inch. They showed a MV of 2,942 for XM193 out of a 16" test barrel. I used 2,950 when I ran the trajectory through the Lee Shooter calculator. The spec for M193 through a 20" barrel is 3,165 fps.

 

[pblanc]

I think that a muzzle velocity less than 3000 fps from a 16 inch barrel is a rather low guesstimate for M193, at least for the more commonly encountered environmental conditions.

The Army specifications for various types of AR 15 rifles and carbines specify a MV of 3250 fps for the M 16 A1 rifle, 3100 fps for the M 16 A2, A3, and A4 rifles, and 2970 for the M 4 carbine.

Of course, the M 16 A1 velocity figure is for M 193, 55 grain ball and a 20" barrel with a 1:12 twist rate. The figures for the M 16 A2,3, and 4 are for a 20" barrel with a faster 1:7 twist rate and M 855 62 grain ball ammo. The figures for the M 4 are for the same 62 grain ammo, and a 14.5" 1:7 twist barrel. And the Army does not specify the environmental conditions (humidity and density altitude) that the velocity figures are based on.

But the muzzle velocity specification for the M 4 carbine shooting the heavier M 855 with a barrel at least 1.5" shorter than civilian carbines is still almost 3000 fps and would certainly be greater than 3000 fps for the 55 grain projectile. The difference in velocity figures for the M 855 62 grain cartridge going from the 20" barrel to the 14.5" barrel given by the Army is 130 fps or about 23.6 fps per inch of barrel loss. The rifleshooter article shows an average velocity loss per inch of 25.7 fps for M 193 and 30.3 fps for M 855, a bit greater loss per inch than the Army figures suggest. I think if you figure a velocity loss of 25 fps per inch loss of barrel length, you will be close for the M 193 round, which would put the muzzle velocity somewhere around 3065-3150 fps for the 16" barrel.

Depending on what type of front sight you have, you are not going to be able to zero elevation precisely enough that a small difference in MV is going to matter all that much anyway. If you have an A1 style front sight post, with 5 detents per complete turn, and a carbine-length gas system, each front sight post "click" is going to shift your point of impact by 1.4 MOA or .35" at 25 yards. But if you have an A2 front sight post, with only 4 detents on the front post flange, each click will change your POI by 1.75 MOA, or .44" per click at 25 yards.

Either way,with no other options to zero elevation with the A1 rear sight (apart from changing the front sight post by grinding a bit off the top) your elevation zero adjustment is going to be rather coarse, so I wouldn't sweat a small error in muzzle velocity estimation.

 

[Aguila Blanca]

http://ballisticsbytheinch.com/223rifle.html

I wrote that the BBTI data were for XM193, but I see that I was mistaken. It's for 55-grain Remington UMC, which may run slower than Lake City XM193.

 

[DMK]

That's great in theory, except that the range I usually shoot at is an indoor range that only goes to 25 yards, and doesn't allow centerfire rifle. Ny testing I do is completely dependent on persuading a friend to get me into the outdoor range he belongs to -- which only goes to 100 yards.

I'm looking to zero for XM193, 55-grain ammo. Running the trajectory for that ammo with the MV for a 16" barrel, the 50-yard zero actually does give a 200-yard zero. At 100 yards I should be 1.37 inches above point-of-aim. That's about the best I can do. But I would much prefer not to waste my friend's time going through a bunch of trial and error with two different apertures. Maybe that's what it will have to be, but I would still hope someone can tell me if the 'L' aperture is up when the sight is flipped forward, or back.

I think you are making things too complicated. I like to keep it easy and simple and use the same zero for all my .223/5.56 ARs and AKs, red dots or irons.

I use a 3" splatter bullseye target and set it up at 100y. I use a 6 o'clock hold and zero so all shots center on the center of the bullseye. That's about 1.5" high at 100y. Use the long range aperture on either the A1 and A2. That's will give you around a 200-250y zero depending on ammo and barrel length. Run it through the Strelek app.

If you are shooting very close range (under 25yards), you can switch to the close aperture for a lower POI to account for the high sight over bore. Or just practice hold overs at close range with the LR aperture.

If you really want to keep things simple, buy the XS Sight systems "Same Plane" Aperture.

I would still hope someone can tell me if the 'L' aperture is up when the sight is flipped forward, or back.

As others said, for the A1 long range aperture, flip the sight forward (front aperture laying flat). For the A1 short range aperture, flip it back (rear aperture laying flat). That is assuming it is installed correctly. I've seen them installed backwards on the A1 (flat side should be towards you, concave towards muzzle). The A2 is opposite in both respects.

Some pictures of the different M16 marked apertures here:

https://www.ar15.com/forums/ar-15/-/123-506964/

 

[kraigwy]

Use to shoot a lot of Combat Rifle when I was in the NG using the M16A1. They are the shot at 100 meters (standing) 200 setting rapid, 300 prone rapid, and 400 yards slow fire prone.

We sighted in at 250 meters. On the 100 and 400 we shot center hold, 6 o'clock hold for the 200 and 300 meters. If the hold was good, all the bullets would stay in the 5 Ring.


In 1978 I attended the USAMU Sniper/Counter Sniper School. Post Vietnam, until the late 80s when the Army's schools got on line, the AMU School was designed to provided instructors for Civilian Leo, and Military unit schools.

In addressing the Civilian Schools the AMU Recommended the 223 Round, which at that time was the 55 gr bullets along the lines of the M193 Military 55 gr round. (And what I carried on my department in a Rem 700 Varmint)

The AMU Recommended the 223 55 gr bullet be sighted in at 250 meters, with the idea of aiming at the mouth chin area, and the bullet would make head shots to 300 meters.

Through the 80s and early 90s I ran Sniper Schools for the AK NG, the Reg Army (Alaska Command) and police departments).

For the civilians we used the 223 bolt guns. Again we sighted them in for 250 meters and with the aiming point suggested by the AMU, the 223s were capable of the head shots to 300 yards. Of course the requirements for LE counter snipers are relatively short range, but if needed the 300 yard capability is there.

Everyone has their valid opinions, but I still use the 250 meter zero for my 1:12 twist 223 Rifles. It worked for me and I have other twist (1:7 & 1:8s),