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Posted: 12/11/2005 6:39:23 PM EDT
About a week and a half ago I asked how people employ their irons. I also suggested that it seemed that the bigger aperture would be the way to go for close up work. I think only one of you stated that you use your bigger aperture out to 200 yards. A couple of you snided at me for being ignorant. And the rest of you just shared what works for you. I thank you all and wanted to share an article in SOF about the way they trained I MEF Marines at Gunsite. It sounds like the teachings were a joint effort between the marines and Col. Bob Young, Vice President of Gunsite.

"One Marine Corps Known-Distance Marksmanship myth that was broken during the Gunsite training was about the purpose of the large-aperture rear sight. Almost all Marines are taught that the rear sight is only for low or no light use. This is not true. The large aperture rear sight is for engaging targets between 0 and 200 meters. The small aperture is for engaging targets from 200 meters and beyond. Also, the large aperture is not on the same plane as the small aperture, thus will not shoot to the same point of aim, point of impact. The small / "long range" aperture is approximately 6 Minutes of Angle (MOA) higher than the larger / "short range" aperture. Knowledge of this fact is very important so that Marines can adjust elevation accordingly."


I know everybody has their ways and that's fine with me, but at least I know I'm not crazy. Now if I can just learn to hit anything at 200 yards with the big aperture!!!!


BTW, today I confirmed that the large aperture is right around what he said. I was shooting at 50 yards and when I changed it to the larger it was like 3-4" lower.

Take it for what it's worth and if you want to read the article yourself it's the January 2006 issue of Soldier of Fortune on bookstands now.
Link Posted: 12/11/2005 6:43:52 PM EDT
The MTT was put together to support a Wing Support Squadron. Its CO goes out there to teach every once in a while and sends his troops out there on the Government's dime.
Link Posted: 12/12/2005 6:53:20 AM EDT

Originally Posted By JJREA:
About a week and a half ago I asked how people employ their irons. I also suggested that it seemed that the bigger aperture would be the way to go for close up work. I think only one of you stated that you use your bigger aperture out to 200 yards. A couple of you snided at me for being ignorant. And the rest of you just shared what works for you. I thank you all and wanted to share an article in SOF about the way they trained I MEF Marines at Gunsite. It sounds like the teachings were a joint effort between the marines and Col. Bob Young, Vice President of Gunsite.

"One Marine Corps Known-Distance Marksmanship myth that was broken during the Gunsite training was about the purpose of the large-aperture rear sight. Almost all Marines are taught that the rear sight is only for low or no light use. This is not true. The large aperture rear sight is for engaging targets between 0 and 200 meters. The small aperture is for engaging targets from 200 meters and beyond. Also, the large aperture is not on the same plane as the small aperture, thus will not shoot to the same point of aim, point of impact. The small / "long range" aperture is approximately 6 Minutes of Angle (MOA) higher than the larger / "short range" aperture. Knowledge of this fact is very important so that Marines can adjust elevation accordingly."


I know everybody has their ways and that's fine with me, but at least I know I'm not crazy. Now if I can just learn to hit anything at 200 yards with the big aperture!!!!


BTW, today I confirmed that the large aperture is right around what he said. I was shooting at 50 yards and when I changed it to the larger it was like 3-4" lower.

Take it for what it's worth and if you want to read the article yourself it's the January 2006 issue of Soldier of Fortune on bookstands now.



The results of your range outing mirror mine.
Link Posted: 12/12/2005 12:06:35 PM EDT
This is not news. The large aperture is not marked 0-2 on a whim. People may use their sights in different ways, but the A2 rear sight was designed with the large aperture intended for 0-200 meters and the small for 300+ meters. Read the Army's operators manual TM9-1005-319-10 , specifically page 47.

Link Posted: 12/12/2005 12:09:03 PM EDT
Does anyone know if the ARMS 40 BUIS is like this as well?
Link Posted: 12/12/2005 12:21:33 PM EDT

Originally Posted By zrxc77:
This is not news. The large aperture is not marked 0-2 on a whim. People may use their sights in different ways, but the A2 rear sight was designed with the large aperture intended for 0-200 meters and the small for 300+ meters. Read the Army's operators manual TM9-1005-319-10 , specifically page 47.




+1
Link Posted: 12/12/2005 12:25:59 PM EDT
Hot diggety!

I wasn't doing it wrong, then (I was the lone big aperture user)

WIZZO
Link Posted: 12/12/2005 12:29:06 PM EDT
Col. Young was the Operations Manager at Gunsite, but retired. He was replaced by Rangemaster Ed Head.
Link Posted: 12/12/2005 12:50:39 PM EDT

Originally Posted By Nemesis_318:
Does anyone know if the ARMS 40 BUIS is like this as well?


It depends on which specific model you purchase. They offer versions with a 250-300 meter aperture and a 500-600 meter notch, versions with a standard A2 peep that has 0-200 meter and 300+ meter apertures, and versions with same-plane apertures that switch between large and small apertures with no shift in POA/POI:

www.armsmounts.com/catalog.php?action=110&cat_id=4

Link Posted: 12/12/2005 1:13:55 PM EDT
Wow, so not news to me, but thanks for sharing.

As an aside- Ever had an eye exam?

....Where they ask you to read the chart for the second time, only this time you are looking through that dial they hold to your eye, and it's a very small hole? It helps you focus better at longer distances, and helps the eye-tech guage whether you are near-sighted or far-sighted or having a temporary problem.

Just thought I'd toss that out there...

- rem
Link Posted: 12/12/2005 5:02:34 PM EDT

Originally Posted By zrxc77:
This is not news. The large aperture is not marked 0-2 on a whim. People may use their sights in different ways, but the A2 rear sight was designed with the large aperture intended for 0-200 meters and the small for 300+ meters. Read the Army's operators manual TM9-1005-319-10 , specifically page 47.




I realize this. I think I first read it in my colt owners manual. But when I posted a thread about 1-1/2 ago, asking people what they do, I was shunned by a couple people when I suggested it seems like the larger would be faster / better for closer distances. In fact, one of them called me ignorant. Although he seemed to mistake me for someone who was arguing with him about shooting MOA with the irons in a different thread I'm guessing. But nevertheless, this practice seems to not be the norm among arfcom people and even a couple of them were military. So I thought I'd share.


Wizzo, bravo!!!!!! Can you hit anything at like 100 yards with the big aperture?? I've got to do some more practicing.
Link Posted: 12/12/2005 5:12:48 PM EDT
[Last Edit: 12/12/2005 5:13:27 PM EDT by hispeedal2]
This is standard use in the military side of the house.

although................


I have recently had problems focusing on that 300M pop up and I have decided that I need to use the small aperature.

I checked my speed on the Engagement Skills Trainer (EST) 2000 and found not only was I just as quick with the small but, I was still faster than all those young punks.
Link Posted: 12/12/2005 5:20:21 PM EDT
[Last Edit: 12/12/2005 5:22:19 PM EDT by DougW]
I have always used the 0-200 for nearly everything, and I was certain (now confirmed) that the small apature caused a different POI. I was able to hit man sized poppers at 250 yards with the 0-200 at the last 3 gun, and the next time I will know to flip the sight for longer than 200 yards (I just had new glasses made for shooting, and it helped). Thanks for the info.
Link Posted: 12/12/2005 5:45:58 PM EDT

Originally Posted By JJREA:

Wizzo, bravo!!!!!! Can you hit anything at like 100 yards with the big aperture?? I've got to do some more practicing.



Yeah, I can keep about 3-3.5" groups at 100 with Wolf. I haven't tried any better ammo so I don't really know what I'm capable of. I'm used to shooting dirt clods in our field and dirt is a hell of a lot more reactive than paper. It gives me instant feedback to where I'm hitting in relation to where I'm aiming and I think this is where I've learned how to use the big aperture.

WIZZO
Link Posted: 12/12/2005 6:02:49 PM EDT
Some may benefit from visiting thezeroing page of The Maryland AR15 Shooter's site.


Does anyone know if the ARMS 40 BUIS is like this as well?


Yes, the ARMS #40 is exactly like this unless you order it with a same-plane aperture.

I'm kind of surprised that this many shooters haven't yet realized there is a significant difference in point of impact between the large aperture and the small aperture on standard sights.

I'd also recommend the IBZ over the 25/300 zero taught by the Army that the A2 sight is designed for...
Link Posted: 12/12/2005 8:56:23 PM EDT

Originally Posted By WIZZO_ARAKM14:

Originally Posted By JJREA:

Wizzo, bravo!!!!!! Can you hit anything at like 100 yards with the big aperture?? I've got to do some more practicing.



Yeah, I can keep about 3-3.5" groups at 100 with Wolf. I haven't tried any better ammo so I don't really know what I'm capable of. I'm used to shooting dirt clods in our field and dirt is a hell of a lot more reactive than paper. It gives me instant feedback to where I'm hitting in relation to where I'm aiming and I think this is where I've learned how to use the big aperture.

WIZZO



That's pretty dang good, what loading of wolf do you use?
Link Posted: 12/12/2005 9:08:32 PM EDT
I use the Santose IBZ on my carbine. I use the small aperture, but can use the large aperture on the same plane by clicking the elevation wheel 4 clicks.
Link Posted: 12/12/2005 9:17:45 PM EDT

Originally Posted By remedy:
Wow, so not news to me, but thanks for sharing.

As an aside- Ever had an eye exam?

....Where they ask you to read the chart for the second time, only this time you are looking through that dial they hold to your eye, and it's a very small hole? It helps you focus better at longer distances, and helps the eye-tech guage whether you are near-sighted or far-sighted or having a temporary problem.

Just thought I'd toss that out there...

- rem



Yes, they asked me to read the chart. I said "what chart"? "The chart on the wall", they said. I said "what wall"? And the answer is, yes, I now have corrective lenses.
Link Posted: 12/12/2005 9:23:12 PM EDT
[Last Edit: 12/12/2005 9:23:55 PM EDT by WIZZO_ARAKM14]

Originally Posted By JJREA:

That's pretty dang good, what loading of wolf do you use?



It was the 55gr FMJ loading out of my RRA 20" A4 w/detachable carry handle with a 1/9 twist chrome-moly barrel.

WIZZO
Link Posted: 12/13/2005 4:42:17 AM EDT
This is probably a dumb question, but given the two-plane design, wouldn't it have made more sense to have the larger aperture hit higher rather than lower than the smaller aperture? Reason I ask is that whichever zeroing method you use, you set it against the smaller aperture. You then flip to the larger, and at the ranges you're supposed to use that aperture, you hit way lower. Given the two options I would think it would have made more sense to have it hit a bit higher, especially since the range envelope for using the large aperture is in close. I guess if I'm shooting something from 50 yds in, I'd rather it not hit low -- I'd rather just sight in on COM and know that the bullet will hit a tad higher where all the vital target area sits. The flip side of course is that at 150-200, maybe it would too high.

Having said that, I never understood why they didn't design it with a same plane aperture to start. If using a same plane, do conventional zeroing methods or IBZ methods still work?
Link Posted: 12/13/2005 4:50:03 AM EDT

Originally Posted By JJREA:
But when I posted a thread about 1-1/2 ago, asking people what they do, I was shunned by a couple people when I suggested it seems like the larger would be faster / better for closer distances. In fact, one of them called me ignorant.



NO! Not on arfcom!

Link Posted: 12/13/2005 5:22:20 AM EDT
I missed the first thread, but I am amazed that nobody knew this. RTFM, it's right there. It's on the damn sight itself, WTF? It's what is behind the whole ghost ring sight concept.
BTW, I use the ARMS 40 LP/SP rig, and it's pretty close to being right on the same plane. I use the large ap for pretty much everything with an M68 cowit, and it gripes my ass that the small plane is the default when you deploy the 40.
Link Posted: 12/13/2005 6:04:47 AM EDT
Im curious as to the reason POI goes 6 moa down when using the ghost ring. Perhaps it suits a certain shooting position better than others? If there is a good reason for it to be designed that way I would like to hear it.
Link Posted: 12/13/2005 6:52:42 AM EDT

Originally Posted By Zaitev:
Im curious as to the reason POI goes 6 moa down when using the ghost ring. Perhaps it suits a certain shooting position better than others? If there is a good reason for it to be designed that way I would like to hear it.



The change in POI seems to be variable, and dependant on barrel length. XS Sights has documented at least 3 different offsets in the A2 apertures.

An offset was a decent idea if you correctly zeroed the small aperture for 300m, then flip to the large aperture for a 200M zero. However the later apertures seem to have a larger offset. I wonder if it's dut to the manufacturers figuring out the Army Zeroing method doesn't produce a real 300M zero (it's a bit further out) or if it's just manufacturing tolerances?
Link Posted: 12/13/2005 7:14:04 AM EDT
I can't hit jack shit with the large aperature. My groups open WAY the hell up with that puppy.

I should have picked the same plane #40, but I wasn't aware of the option. The only reason I would ever swing that guy up is for low light.

That said I was aware of the offset and it is obvious when shooting from a bench.
Link Posted: 12/13/2005 8:00:03 AM EDT
Zaitev, jmart and others who are still having trouble understanding the dual apertures: I think you are missing the point that the apertures were designed to be used at different ranges and in conjunction with the elevation wheel. The large aperture is to be used for 0-200 meter ranges with the elevation wheel turned all the way to the bottom. The small aperture is to be used for 300-800 meter ranges witht elevation wheel turned to match the target range. By using the different apertures together with the elevation wheel, you can maintain a pretty consistent POI over the entire operating range of the rifle, but only if you actually set them properly for the range of your target.

Have you ever used an adjustable leaf site like on a Mauser? It is the same basic principle, but implemented a little differently. Perhaps it will help you understand better:



Notice the marks for range (in hundreds, I believe). As you move the tab to more distant ranges, it elevates the sight to compensate for the bullet trajectory's drop at longer ranges.

Now, imagine that you have the sight set to 300 meters as shown and zero your rifle against a target 300 meters away. The bullets impact right in the center of your target. Now you adjust the sight to the 700 meter setting, but you continue to shoot at the target 300 meters away. Would you have any reason to expect that the bullets would continue to impact in the bullseye at 300 meters? Of course not. They would be hitting high. However, if you now walked your target out to 700 meters then you again would be hitting it in the bullseye.

The same thing applies to the A2 rear sight, and flipping the apertures is equivalent to changing the range setting. There is no reason to expet that the POI will remain the same at the same range when you switch apertures, because the apertures are calibrated for use at different ranges.

The basic principle of the A2 sight is the same as the Mauser's adjustable leaf sight: you move the rear sight higher/lower for longer/shorter ranges. The only difference with the A2 sight is that, since the wheel only goes down to a 300 meter setting, the larger aperture also incorporates an offset to shift the POI for proper use at 0-200 meter ranges. Perhaps some confusion arises because of this dual function of the larger aperture. It not only gives a more open sight picture for faster acquisition in CQB, but it also includes an offset to adjust the POI for use at 0-200 meter ranges.

Why didn't the designers decide to add additional threads and travel to the elevation wheel so that it could go all the way down to 0 meters? That I do not know. If they did, then they could have put the two different apertures on the same plane with no offset and switching between the two would change nothing but the size of the aperture. However, the reality is that the designers did stop the elevation wheel at 300 meters and switching to the larger aperture does include additional offset to compensate for the bullet trajectory at close-in 0-200 meter ranges.

Please read through the links I and Bartholomew_Roberts posted earlier in this thread. I think if you read carefully it will clear up all your questions.
Link Posted: 12/13/2005 8:08:10 AM EDT

Originally Posted By Forest:
The change in POI seems to be variable, and dependant on barrel length. XS Sights has documented at least 3 different offsets in the A2 apertures.

An offset was a decent idea if you correctly zeroed the small aperture for 300m, then flip to the large aperture for a 200M zero. However the later apertures seem to have a larger offset. I wonder if it's dut to the manufacturers figuring out the Army Zeroing method doesn't produce a real 300M zero (it's a bit further out) or if it's just manufacturing tolerances?


Forest, I wouldn't be surprised if the different offsets in different A2 apertures are designed to compensate for the different barrel lengths (and thus sight radii and trajectory). Without doing detailed measurements and calculations, the ratio of the 0.017 and 0.024 figures you quote on your website seems to match, to first order, the ratio between 14.5 and 20 inch barrels.

Link Posted: 12/13/2005 8:13:35 AM EDT

Originally Posted By m24shooter:
I use the large ap for pretty much everything with an M68 cowit, and it gripes my ass that the small plane is the default when you deploy the 40.


ARMS states that you can remove the small aperture from the #40 L SP. You might want to consider doing this. It sounds like you wouldn't miss the smaller aperture since you pretty much use only the larger aperture, and you wouldn't be bothered anymore with the small aperture being the default when you deploy the sight.
Link Posted: 12/13/2005 8:20:10 AM EDT

When I use the large aperture my groups move off the black and to the right side of the target. What am I doing wrong?

In Army Basic they only taught us small aperture use. With qualification targets 50-300m they wanted to be sure we would still hit the far targets.
Link Posted: 12/13/2005 9:12:01 AM EDT

Originally Posted By Robert2011:
When I use the large aperture my groups move off the black and to the right side of the target. What am I doing wrong?


I can think of two possibilities for a shift in windage:

1. You aren't centering the front sight post consistently with the two different apertures. It is a little harder to center with the larger aperture. Usually I would expect this to result in simply opening up the groups, not shifting them, but you could have a systematic difference in how you position the sights when using the two different apertures.

2. Your aperture assembly is faulty. In addition to the elevation offset difference between the two apertures that we have been talking about, there is also a windage offset. This offset is needed to compensate for the fact that the aperture assembly rotates on a threaded screw and thus actually shifts a small amount left-to-right/right-to-left when you switch between the apertures. If everything is set up properly, the windage offset exactly compensates for the movement of the assembly on the thread and there is no change in the POI's windage.

When you flip from the small aperture to the large aperture the aperture assembly moves to the left, so I would normally expect that if the offset isn't accounted for the POI would also shift left. If yours is bad, it would have to be so bad that it overcompensates for shift in the aperture assembly. Less likely than undercompensation, but possible.

To try to narrow it down, try shooting both apertures of someone else's rifle and have that person shoot both apertures of your rifle. This should tell you whether the problem is with the rifle or the shooter.
Link Posted: 12/13/2005 10:12:21 AM EDT
[Last Edit: 12/13/2005 10:26:30 AM EDT by jmart]

Originally Posted By zrxc77:
jmart and others who are still having trouble understanding the dual apertures:

The only difference with the A2 sight is that, since the wheel only goes down to a 300 meter setting, the larger aperture also incorporates an offset to shift the POI for proper use at 0-200 meter ranges. Perhaps some confusion arises because of this dual function of the larger aperture. It not only gives a more open sight picture for faster acquisition in CQB, but it also includes an offset to adjust the POI for use at 0-200 meter ranges.

Why didn't the designers decide to add additional threads and travel to the elevation wheel so that it could go all the way down to 0 meters? That I do not know. If they did, then they could have put the two different apertures on the same plane with no offset and switching between the two would change nothing but the size of the aperture. However, the reality is that the designers did stop the elevation wheel at 300 meters and switching to the larger aperture does include additional offset to compensate for the bullet trajectory at close-in 0-200 meter ranges.




Here's what's not making sense to me: whether using IBZ technique or miltary technique, you are basing your zero on the smaller aperture. Set rear elevation bottomed out (or minus 2/4 clicks for IBZ) and then adjust front post to adjust vertical POI at your zero range. So far, so good.

But then for in close, you switch to the larger. In doing so, you screw up your zero to around 6 MOA low. I've never shot using the large out to 200, where do impacts occur out there? Does vertical POI coincide with your aimpoint or is there still some elevation delta? If so, how much? Does the large aperture work better if you zero by the manual instead of using an IBZ?

Regardless, as I see it, the real issue manifests itself when shooting in close. POI is well below your aimpoint, and that just doesn't make sense to me. Why they didn't drill the aperture so that vertical POI coincides with a 50 yd aimpoint, and then again around 200, is beyond me. Maybe I'm looking at this too much like the IBZ process, in which case it would seem the same plane would be the obvious answer.

At this point it's purely academic. My current setup is EoTech with a LaRue BUIS, front sight post set for 50 yd zero using the small aperture. Wheel adjusting isn't an option thank God. I haven't done much work with the large aperture since I'm just plinking/practicing in the middle of the day and lighting is never an issue. Frankly, unless the lighting is pretty poor, I couldn't imagine not using the smaller aperture from 50 on out, and reserving the large aperture for 50 and under. But after I heard months ago about the shift in impact point, I've never been too enthused about doing much practice with the large aperture. If I were to start using it more, I'd probably readjust my front post to zero with the large aperture at 50.

ETA: This is from Chuck Santose' IBZ proc from the earlier link. The Maryland site editor acknowledges that when flipping to the large aperture, you may have to adjust the elevation wheel up four to six clicks to get the large aperture's trajectory to coincide with the trajectory established using the IBZ process using the smaller aperture. My point is you should never have to adjust any elevation setting to get things to coincide -- the large aperture should be drilled at the right heigth to make sure this happens.


If you're patrolling, set the sight to 8/3 and snap the aperture forward to 0-2. This will provide the same trajectory as above but with a larger, easier to see thru rear sight. Use this setting if you also have the M68 mounted as it's quicker to transition to if the sight fails. [Editor's Note - there is some variance with the offset of the A2 aperture - they SHOULD be a 2 click difference - however some manucatures produce them with larger offsets. Setting the sight to 3 then flipping to 0-2 might now work for your AR. Check it at the range, you want the group to be centered at 50y, you might need to set the sight at 3 +2 or even 4 to get the large aperture to be correct]
Link Posted: 12/13/2005 11:34:30 AM EDT
[Last Edit: 12/13/2005 2:33:16 PM EDT by zrxc77]

Originally Posted By jmart:
Maybe I'm looking at this too much like the IBZ process, in which case it would seem the same plane would be the obvious answer.


Yes, I think you hit it there. You are thinking in terms of the IBZ but the sights were designed for a military zero that is different than the IBZ. The fundamental difference being that the IBZ was designed to provide an adjustment-free, relatively flat trajectory out to 250 meters or so at the expense of long-range capability, while the military zeros were designed to provide a relatively flat trajectory out to 800 meters at the expense of requiring adjustment of the elevation wheel and apertures.

Check out the trajectories page from Forest at the Maryland AR15 Shooters' Site. For example, lets look at the trajectory for M855 out of a 20" barrel. Forest can correct me if I am wrong, but I believe these show the trajectories when fired using the small aperture with the elevation wheel set at 8/3 (or 6/3 for detachable carry handles) and zeroed according to the respective zeroing methods:



Notice that the IBZ trajectory is pretty flat out to around 275 yards (250 meters) after which it drops off fairly quickly. The standard Marine trajectory, on the other hand, is zeroed at about 330 yards (300 meters) and doesn't fall off as quickly at longer ranges. However, it peaks up higher at shorter ranges.

What does this all mean? The A2 sights are designed to compensate for the trajectory when using the standard zero. Thus if the rifleman with a Marine zero needs to engage a target at 500 meters, he dials his elevation wheel to 5 and, using the small aperture, the trajectory drop is compensated so that POI equals POA at 500 meters. The rifleman with the IBZ, on the other hand, is out of luck at 500 meters. Turning the elevation wheel to 5 would only bring the POI up about 28 inches while the IBZ trajectory needs to be brought up closer to 40 inches. <edit> In a post following this post Forest corrected me and indicated that the wheel markings will match up to actual ranges at longer ranges with the IBZ and the POI will be brought up the proper amount. </edit>

The flip side is that the rifleman using the Marine zero is about 6 inches high at 200 meters when using the small aperture with the elevation wheel at 3. However, this Marine rifleman would not use the small aperture at such short ranges. Instead, he would flip to the large aperture which lowers POI 6 inches to compensate for the trajectory and, viola, he is back on target. In contrast, the IBZ rifleman doesn't have to adjust his small aperture at all for 200 meter and closer ranges. However, if he flips to the large aperture because he wants a larger field of view, he will have to adjust his elevation wheel because the larger aperture includes an offset to compensate for the trajectory of the military zeroing method it was designed to be used with, not the IBZ.

In summary, when used as originally intended, the elevation offset between the large and small apertures allows the rifleman to consistent zero from 0 meters out to 800 meters. That it was the sight was intended to do: allow accurate fire at short and long distances when properly ranged. The IBZ takes a different philosphy and provides a hands-free zero that gives good accuracy to 250 meters or so but has no real capability at longer ranges. *

Thus, these are two different zeroing methods with two different philosophies and characteristics. You are correct that a single-plane set of apertures would make more sense for an IBZ zero, but you are forgetting that the sights were not designed to use the IBZ zero.

A shorter summary is that the designers knew what they were doing, did not make decisions arbitrarily, and designed according to the requirements at the time. If requirements have changed since then, you can't blame them for making the choices they did at the time they did with the information they had.

* Yes, the IBZ could be adjusted with the elevation wheel to provide accurate fire at longer distances, but the standard markings would not apply. For example, you might need to set the wheel to 7 in order to hit at 500 meters. But you would have to figure this out empirically at all ranges you wish to engage and re-mark the wheel or memorize the different settings - not very convenient and not really how the IBZ was intended to be used. <edit> In a post following this post Forest corrected me and indicated that the wheel markings will match up to actual ranges at longer ranges with the IBZ. </edit>

(Also note that everything changes with different loads and barrel lengths as well since they will have different trajectories. But I believe that at the time the A2 sight was designed there was only one standard round and barrel length in common use and doctine still emphasized long-range shooting, so the sight was designed to match that trajectory for that purpose.)
Link Posted: 12/13/2005 1:04:46 PM EDT
I don't understand why the front site post isn't just a fixed post and all the adjustments are made with the rear site windage and elevation wheels. (like a revolver) Seems it would be easier with that system using two aperatures with the same plane?

I just attempted to zero my buis using the info on the Bushmaster target. It had me raising and/or lowering the front site post using the small ap one click up from the bottom 300 m setting. Of couse when I flipped the ap to the 0-200 it was all screwed up shooting lower; (like it was supposed too)

I would prefer to have my iron sites set up for 100 yards no matter which ap I used. Then I could just raise the front site post a little higher on my target and/or turn my rear elevation knob up accordingly for longer distance targets.

If one could zero their rifle for one hudred yards and then just turn the elevation knob to whatever yardage they watned, it would be a lot easier. Note, this doesn't take into consideration different length barrels, bullet weights etc. but each person could tweak their own sites from a common zero that way.....say a 16" inch barrel...
Link Posted: 12/13/2005 1:18:10 PM EDT

Originally Posted By zrxc77:

Originally Posted By jmart:
Maybe I'm looking at this too much like the IBZ process, in which case it would seem the same plane would be the obvious answer.




.... The flip side is that the rifleman using the Marine zero is about 6 inches high at 200 meters when using the small aperture with the elevation wheel at 3. However, this Marine rifleman would not use the small aperture at such short ranges. Instead, he would flip to the large aperture which lowers POI 6 inches to compensate for the trajectory and, viola, he is back on target. In contrast, the IBZ rifleman doesn't have to adjust his small aperture at all for 200 meter and closer ranges. However, if he flips to the large aperture because he wants a larger field of view, he will have to adjust his elevation wheel because the larger aperture includes an offset to compensate for the trajectory of the military zeroing method it was designed to be used with, not the IBZ.

In summary, when used as originally intended, the elevation offset between the large and small apertures allows the rifleman to consistent zero from 0 meters out to 800 meters. That it was the sight was intended to do: allow accurate fire at short and long distances when properly ranged. The IBZ takes a different philosphy and provides a hands-free zero that gives good accuracy to 250 meters or so but has no real capability at longer ranges.




Thanks, that's the clearest explanation I've read that describes why the shift was designed into the two apertures.

Given this explanation, then even if you are dealing with a non-elevation adjustable BUIS (e.g., LaRue), then would it make the most sense to zero just like the manual says, use the small for 200 and out, hold COM out to 375, and use the large aperture for 200 and in, correct?
Link Posted: 12/13/2005 1:22:55 PM EDT
The LaRue Buis has same plane appertures. Zero for 200m and learn the holdovers to 400m or farther.
Link Posted: 12/13/2005 1:25:23 PM EDT
[Last Edit: 12/13/2005 1:26:27 PM EDT by jmart]

Originally Posted By Combat_Jack:
The LaRue Buis has same plane appertures. Zero for 200m and learn the holdovers to 400m or farther.



Are you sure? I would have sworn that LaRue's are dual-plane.

Grant?
Link Posted: 12/13/2005 1:38:45 PM EDT

Originally Posted By zrxc77:
[* Yes, the IBZ could be adjusted with the elevation wheel to provide accurate fire at longer distances, but the standard markings would not apply. For example, you might need to set the wheel to 7 in order to hit at 500 meters.



That is entirely incorrect.

If you zero with LTC Santose's instructions the wheel will be properly calibrated giving you the ability to make hits at 200, 300, 400, 500, etc by setting the wheel and using the small aperture (bottomed out will be 200).

If you want to use the large aperture - not problem. If the 300M setting doesn't work for your model then keep clicking up and testing it to find when your large aperture zeros at 50y. Then leave it there.

BTW this whole issue is moot if you just spend the $30 and get an Ashely same plane rear aperture.
Link Posted: 12/13/2005 1:46:59 PM EDT
[Last Edit: 12/13/2005 1:47:26 PM EDT by Forest]

Originally Posted By zrxc77:
For example, lets look at the trajectory for M855 out of a 20" barrel. Forest can correct me if I am wrong, but I believe these show the trajectories when fired using the small aperture with the elevation wheel set at 8/3 (or 6/3 for detachable carry handles) and zeroed according to the respective zeroing methods:


Those show the trajectories as if you followed the instructions. Ballistics don't care what the handle values are (if any) or what aperture you use - that stuff is only important for humans.

However I'll summerize it.

1) A1 zero - use the unmarked aperture on an M16A1 (after zeroing with the L aperture)
2) A2 Army Zero - using the small aperture with the elevation wheel set to '3' (zeroed at 25m w/ offset)
3) A2 Marine Zero - using the small aperture with the elevation wheel set to '3' (zeroed at 36y)
4) Bubba Zero - using the small aperture with the elevation wheel set to '3' (zeroed at 25y)
5) IBSZ - using the small aperture with the elevation wheel set to '3' -2 (fixed) or -4 (detachable).
Link Posted: 12/13/2005 1:51:23 PM EDT

Originally Posted By NRA2:
I don't understand why the front site post isn't just a fixed post and all the adjustments are made with the rear site windage and elevation wheels. (like a revolver) .



Because you'd have an issue returing the site to a 'baseline' state. Each rifle would need to have it's battlesight zero at a different height. Not good when another soldier might be using your rifle (and not know it).

The front sight is adjusted so when your rifle is at '3' it means 300M, just as if you pick up your buddies rifle and set it to '3' it will have a 300M zero.

If adjustments were made at the rear along with elevation changes then setting the rifle to '3' on my rifle may mean 400y, but setting it to '3' or your rifle might mean 250y.

Personally I think the AR front sight adjustment is pure brilliance - I wish my 'civilian' rifles were as easy to zero.
Link Posted: 12/13/2005 1:54:56 PM EDT

Originally Posted By NRA2:
I don't understand why the front site post isn't just a fixed post and all the adjustments are made with the rear site windage and elevation wheels. (like a revolver) Seems it would be easier with that system using two aperatures with the same plane?


First, where you adjust the elevation while zeroing (front or rear sight) is a completely separate issue from dual-plane versus single-plane rear apertures. Neither design decision affects the other.

Second, handguns can get away with a single elevation adjustment at the rear sight because handguns are generally designed for use only at such short ranges that compensation for bullet drop as a function of range is neither needed nor desired. You don't normally see range markings on handgun sights (Exceptions made for such overly ambitious examples as the broomhandle Mauser ) :



If you did both elevation zeroing and range compensation with the rear sight on a rifle, then you could expect that the numbering would be off. For example, you may need to set the dial to 4 in order to zero at 300 meters. But for range compensation you would want it to read 3. To get it line back up to 3 you would then need a separate mechanism for zeroing with the rear sight as opposed to setting range to compensate bullet drop. At that point it is simpler to just handle elevation zeroing with a screw-in front sight post.


Originally Posted By NRA2:
I would prefer to have my iron sites set up for 100 yards no matter which ap I used. Then I could just raise the front site post a little higher on my target and/or turn my rear elevation knob up accordingly for longer distance targets.


And there is nothing wrong with that if that is what works best for you. But the military decided that isn't what they wanted. So you will just have to substitute a same-plane aperture for the standard military daul-plane aperture. Fortunately, with the large civilian market for AR-15 accessories, that isn't a problem.
Link Posted: 12/13/2005 2:11:55 PM EDT
[Last Edit: 12/13/2005 2:42:52 PM EDT by zrxc77]

Originally Posted By Forest:

Originally Posted By zrxc77:
[* Yes, the IBZ could be adjusted with the elevation wheel to provide accurate fire at longer distances, but the standard markings would not apply. For example, you might need to set the wheel to 7 in order to hit at 500 meters.



That is entirely incorrect.

If you zero with LTC Santose's instructions the wheel will be properly calibrated giving you the ability to make hits at 200, 300, 400, 500, etc by setting the wheel and using the small aperture (bottomed out will be 200)


My mistake. I read too much into the statement "This battlesight zero is valid to 300 meters for both the M16A2 and M4 Carbines and their AR15 sisters" on the Maryland AR15 Shooters site. I took that to mean that it wasn't valid beyond 300 meters, and assumed that the reason was because the wheel didn't match up with the actual range at longer ranges. I know the instructions say to zero at 200 m with the wheel at 8/3 - 2, but it wasn't sinking into my head that 8/3 - 2 is precisely where 200 m would be marked in the progression of range settings if the wheel were marked for 200 m. I will edit my previous post to note your correction. Could you double-check my edit to ensure I am not spreading any more misinformation? Thank you.

P.S. Would it be correct to summarize that the main differences of the IBZ method are:

1. Creates a new, unmarked 200 meter position on the elevation wheel at 8/3 -2 to use with the small aperture.
2. Leaves the "default" elevation position at 200 meters to give a flatter trajectory out to 250 meters without adjusting anything (as opposed to the trajectory that the 300 meter position would give).
Link Posted: 12/13/2005 2:35:20 PM EDT

Originally Posted By Forest:
Those show the trajectories as if you followed the instructions. Ballistics don't care what the handle values are (if any) or what aperture you use - that stuff is only important for humans.


They care in the sense that if you fire at a target 300 meters away with the handle set to 3 and then fire at that same target with the handle to set to 5 you are going to get entirely different trajectories (assuming point of aim through the sights is the same for both shots). I think we are saying the same thing. The charts show the trajectories for the default position of the zeroed sights according to the specific instructions (as you have summarized - thank you).
Link Posted: 12/13/2005 3:05:28 PM EDT
.
Link Posted: 12/13/2005 4:08:22 PM EDT
Just the other day I was pondering on the evolution of iron sights on weapons and doing a little brainstorming/day dreaming on the subject.

The idea that all adjustment could/should be made from one point is sound. Less to go wrong, plus its just a PITA to adjust the front sight (generically speaking, no bad on the AR) Simpler is better.

HK does employ their rotating sigt that dials in the right range. I'm not familiar on how they zero it.

Why not simply add a second elevation wheel? Place the rear sight assembly on top of a "range" wheel assembly that will move the rear sight assembly (windage and elevation wheels) up and down to dial in the correct range. Same thing as the elevation you say? Well the function is the same, but the elevation wheel is now only used for zeroing the rifle.

Thus your zero should be maintained as you switch ranges. Plus it would allow easy ranging with a large wheel marked off with ranges. If you follow the proper zero procedures for whatever range your set on, it shouldn't matter which particular range setting you zero on. Only got a 25y or 25 m space. Dial down to 25m on the range wheel, then adjust the windage and elevation wheels to zero.

Thoughts? It doesn't seem overly complicated to me, plus it seems like from the chairborne perspective to be easier to use in combat. The ranges would be clearly marked in numbers on the range wheel. Much easier to switch back and forth, no need to remember what the rifle is set on.
Link Posted: 12/13/2005 4:26:46 PM EDT
Why do you need to adjust your sights after you zero? If its too far to hit with a 200m zero and good knowledge of holdovers, you aren't going to hit it in the field even if you CAN adjust your sights.
Link Posted: 12/13/2005 4:29:04 PM EDT

Originally Posted By Gunzilla:

Originally Posted By JJREA:
But when I posted a thread about 1-1/2 ago, asking people what they do, I was shunned by a couple people when I suggested it seems like the larger would be faster / better for closer distances. In fact, one of them called me ignorant.



NO! Not on arfcom!




I know, I could hardly believe it!!!!!
Link Posted: 12/13/2005 4:46:20 PM EDT

Originally Posted By Combat_Jack:
Why do you need to adjust your sights after you zero? If its too far to hit with a 200m zero and good knowledge of holdovers, you aren't going to hit it in the field even if you CAN adjust your sights.


So you don't have to estimate holdover, for one reason. I suspect the average person can more consistently set the required elevation with a calibrated sight than an eyeballed holdover. Of course, you still need some means to accurately gauge the range to your target, account for shooting up- or down-hill, cross winds, target velocity, etc. But, why not use every tool available to you to help you do your job better?
Link Posted: 12/13/2005 4:56:46 PM EDT
[Last Edit: 12/13/2005 4:57:53 PM EDT by Combat_Jack]

Originally Posted By zrxc77:

Originally Posted By Combat_Jack:
Why do you need to adjust your sights after you zero? If its too far to hit with a 200m zero and good knowledge of holdovers, you aren't going to hit it in the field even if you CAN adjust your sights.


So you don't have to estimate holdover, for one reason. I suspect the average person can more consistently set the required elevation with a calibrated sight than an eyeballed holdover. Of course, you still need some means to accurately gauge the range to your target, account for shooting up- or down-hill, cross winds, target velocity, etc. But, why not use every tool available to you to help you do your job better?



As far as the military goes, the average infantryman does not shoot his weapon at distances long enough to require sight adjustment and wind estimation. This per shooters who train the military for a living. Either they will not shoot at that distance, or they will not adjust their sights to do so, or they simply do not ever encounter an enemy in the open at such distances. Belt fed weapons and MOS Snipers excepted.

For civilian purposes, competition, etc., get whatever you want.
Link Posted: 12/13/2005 7:08:51 PM EDT

Originally Posted By zrxc77:
P.S. Would it be correct to summarize that the main differences of the IBZ method are:

1. Creates a new, unmarked 200 meter position on the elevation wheel at 8/3 -2 to use with the small aperture.
2. Leaves the "default" elevation position at 200 meters to give a flatter trajectory out to 250 meters without adjusting anything (as opposed to the trajectory that the 300 meter position would give).



That is spot on Brother!
Link Posted: 12/13/2005 7:09:10 PM EDT
[Last Edit: 12/13/2005 7:10:40 PM EDT by jmart]

Originally Posted By Combat_Jack:
The LaRue Buis has same plane appertures.



Not according to Grant, at least not for the units made up to recently. Some changes might be in the works. More to follow.
Link Posted: 12/13/2005 7:13:22 PM EDT

Originally Posted By zrxc77:

Originally Posted By Forest:
Those show the trajectories as if you followed the instructions. Ballistics don't care what the handle values are (if any) or what aperture you use - that stuff is only important for humans.


They care in the sense that if you fire at a target 300 meters away with the handle set to 3 and then fire at that same target with the handle to set to 5 you are going to get entirely different trajectories (assuming point of aim through the sights is the same for both shots). I think we are saying the same thing. The charts show the trajectories for the default position of the zeroed sights according to the specific instructions (as you have summarized - thank you).



Yes we are on the same page. I should have clarified in that the ballistic charts shown assume you have zeroed at a particular range. It does not matter what the handle says or which apperture you used when you zeroed at the indicated range with whatever the current settings are. I hope I'm being clear in this.

It's like saying if you zeroed at 50y with the handle set to '7' would produce the same graph, as zeroing at 50y with the sight set to 8/3 -2. The differences would only show up when you started playing with the elevation dial (which the chard does not show).
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