Which aperture do you use?


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halfded
April 14, 2010, 08:20 PM
Just wanted to see which aperture was preferred on BUIS.

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Broken11b
April 14, 2010, 08:27 PM
All of mine have the 0-200 night aperture and the 25-300 daylight aperture, I keep it on the 0-200 aperture if I have to use it, the night ap works for most engagements and since i usually keep them deployed up and just focus on the red dot, the wide ap is easier to ignore until I need it.

way I see it, if your using it for competition or defense, the 0-200 is faster and can be used in low light, the smaller aperture is near useless in lowlight or for speed.

Ragnar Danneskjold
April 14, 2010, 08:58 PM
I have an Army issue version of the BUIS which only have the small aperture. It's also what I've always used on my issue M4. So it just feels more natural on my AR-15.

Broken11b
April 14, 2010, 09:01 PM
Ragnar, which version did they issue you, the ones I had to use were crap.

desidog
April 14, 2010, 09:19 PM
I was issued crap as well.

I figure the day sight is MOA, and the night sight is MOM.

/Minute Of Man

possum
April 15, 2010, 05:05 AM
i use the Ma tech BUIS linked below and i think it is the same as what Ragnar is talking about. It only has one apeture which is fine with me. It is low profile, adjustable for various ranges, and so far has been a great addition to my ar, and the M4's i have had them on in the Army.
http://www.brownells.com/.aspx/pid=26575/Product/AR_15_M16_USGI_BACKUP_IRON_SIGHT

DMK
April 15, 2010, 10:09 AM
Both.

On some of my carbines I use a Same Plane aperture from XS sight systems (no elevation change when switching from the small 'peep' sight to the larger "ghost ring").

On other rifles I have the smaller 'peep' zeroed at 50y/200m and flipping to the large ghost ring gives me an approximately 100y zero. (I've sifted through a number of apertures in my parts drawer to find ones that work this way).

With an A2 sight that has the elevation wheel, you can calibrate it and can then adjust the wheel so that you can use either aperture at whatever range you wish.


For quick snap shots at close range (under 25-50y), I use the ghost ring. For 50y+ precision shooting, I flip to the smaller aperture.

DMK
April 15, 2010, 10:10 AM
Keep in mind that different standard AR15 apertures have varying elevation changes when flipping from one aperture to another.

FAQ # 4

AR-15/M-16: Rear Sight Elevation Shifts and the need for a Same Plane Aperture Sight

As originally designed the AR-15/M-16 sight system adjusts for windage at the rear assembly and for elevation in the front to zero the rifle to the individual shooter. To obtain the ballistic adjustment needed for longer range shooting the original rear sight had one aperture higher than the other. While this system would not give the shooter an exact elevation adjustment for a specific range, it would under battle conditions put the bullet close enough for government work so to speak.

The new A2 rifles and carbines employ a rear sight system that includes a range cam to allow the shooter to more precisely adjust the ballistic arc to their needs. This system eliminated the need for an elevation shift between the large close quarters aperture and the smaller long-range aperture. However the aperture shift is still with us today.

Comparing some of the rear sights available today there appears to be 3 variations available. The 1st style (and oldest) has a .014 offset. This gives a 2.52 inch shift in point of impact at 100 yards between the two apertures. The 2nd style has a .017 offset, which shifts point of impact 3.06 inches at 100 yards. The 3rd style has a .024 offset giving a 4.36 inch shift in P.O.I.

All of the points of impact shifts shown above are for the standard barrel AR-15/M-16 that has a sight radius of 20 inches. The shorter sight radius (14.5 inches) of the M4 carbine and weapons of similar configuration increase the amount of point of impact shift. The shifts for these shorter sight radius weapons are 3.48, 4.25, 5.96 inches respectively.

The only reason for the various shifts would be for changes in the ammunition used by the military over the course of this weapons employment.

Most people are completely unaware of this elevation change that occurs when the aperture is shifted from one to the other. They just figure that their rifle is doing something strange.

Our aperture sight for this weapon has both the large and small apertures on the same plane so there is no difference in the point of impact when you shift from one to the other. We have also offset one of the apertures by .007 to make up for the sideways movement of the aperture on the windage screw as it pivots.

By installing our same plane rear aperture you now can sight in your rifle using the smaller aperture and shift back and forth between the two apertures as your light and range needs change without having to do mental gymnastics to know where your bullets impact will be.

http://www.xssights.com/faqs.html#faq4

Sediment
April 15, 2010, 12:58 PM
Da beeg wun.

Bartholomew Roberts
April 15, 2010, 01:15 PM
I use the Santose IBZ with my A2 sights and use the small aperture for above 300m/precision/day and the large aperture for moving/low-light.

For my Troy folding rear sights, I have a same plane aperture and zero at 50yds. This puts me within 2.5" of point of aim out to about 250yds with 55gr M193. I just hold about 8" high at 300yds to make hits with irons at that range. I typically don't use irons outside that range unless I am just screwing around, so that works for me. Same principle, use the small aperture for precision/day and the large aperture for moving/light

Zach S
April 15, 2010, 07:05 PM
The large one on my .22 and 9mm. The large one on my 5.56 as well, but it has an EOTech with absolute co-witness.

TeamPrecisionIT
April 15, 2010, 08:10 PM
I use the big one as intended and the little one when the range is beyond 300m.

Damian

Quentin
April 15, 2010, 08:19 PM
Like Bartholomew Roberts, I normally use the IBZ with the small aperture. And the large one for low light conditions. Haven't moved on to optics since the A2 sights are so good.

halfded
April 15, 2010, 08:46 PM
Maybe I should have been more specific.

First, BUIS means Back Up Iron Sights, you A2 guys don't apply here, sorry.

Second, I was referring to BUIS that only have windage adjustment and aren't same plane, of course. Lower 1/3 co-witness should be thrown in the mix too.

So, basically if you were stuck with ONE aperture for a BACK UP sight, which would you choose. I guess the poll's kinda screwed now.

DMK
April 16, 2010, 09:17 AM
Which BUIS are you thinking of?

Most have a standard A2 aperture which flips between a close range ghost ring and a smaller 'peep' sight that is set a little higher for a longer range zero.

Like was said earlier, it is usually recommended to zero the small peep with a Santos IBZ (http://www.m4carbine.net/showthread.php?t=22) (50y/200m zero, giving you +/- 2" out to 250m) and you can flip to the larger aperture for closer range zero, low light, and/or wider field of view.

Of course, you could swap the A2 aperture for an earlier A1 type aperture which has two smaller peep sights at two different elevations. Or an XS Same Plane if you want the same zero for both apertures.


I'm the only one on the thread that mentioned an elevation wheel, and I just brought it up as an alternative for those with fixed carry handles.

halfded
April 16, 2010, 11:25 AM
and you can flip to the larger aperture for closer range zero

Doesn't work that way. I have my A2 sight zeroed (per IBZ) with the small aperture at 8/3-2. In order to be on target at the same range with the large aperture, I have to go to 8/3. That's in increase in elevation, meaning that if you left the setting the same the rifle would shoot lower at the same range, and even lower than that at shorter range. The only way what you said would work is if you zero on the large aperture and use the small aperture for close range. Doesn't make any sense to do it that way though.

The BUIS I'm using is from Samson MFG, sold from Del-ton and Spike's.

DMK
April 16, 2010, 04:38 PM
I have my A2 sight zeroed (per IBZ) with the small aperture at 8/3-2. In order to be on target at the same range with the large aperture, I have to go to 8/3. That's in increase in elevation Yes.

You had to increase the elevation on your wheel to make up for the lower elevation of the large aperture. Col Santos mentions that in his IBZ instructions.


1. Sight should be at 8/3 -2 clicks, that is, all the way down, not up a click. Please note removable handle sights are
marked 6/3 (rather than 8/3); also some are in ‘half-clicks’ as well. There should be 3 clicks between 3 and 4 on the
knob. If there are 6 clicks then the sight needs to be set at –4 clicks (instead of –2).
2. Small aperture, nose to firing handle weld.
3. Distance is 50 yards.
4. Point of aim should be point of impact of bullet.
7. Remember you're adjusting the FRONT SIGHT for elevation, not the rear, and that each click is about 1/2"
(actually a little more) at 50 yards. You won't get it closer than that. Don't frustrate yourself trying.
8. You're done. Leave the sight in this position for 99% of your shooting.
9. If you have to shoot targets you KNOW are 300 meters away or more, just click to the right number on the sight.
10. 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]

halfded
April 16, 2010, 06:53 PM
...Which means I'd be shooting lower than with the small aperture...

Which means and you can flip to the larger aperture for closer range zero is incorrect.

But the discussion of elevation adjustments is a digression here. I'm going to have one aperture to use without sighting in the gun over again, and just want some opinions on which to use. I know what IBZ is, I know the intended purpose of both apertures, and I know that there are same plane sights.

My sight has 2 apertures and no elevation adjustment; it flips up with the large aperture in place (no choice).

DMK
April 16, 2010, 09:30 PM
OK, here's an example of the elevation shift. If I zero at 200m with the small peep, the bullet will also cross at 50y or so. It's an arc right? If I now shoot a group at 100y, it will be about 1.5" high, it's going up towards it's peak. Now, I flip to the ghost ring and shoot a group at 100y. It will be very close to zero and it's at the peak of its arc already. It's not going up anymore from there. Now if I shot at 200y with the larger ring, I'll be about 2-3" low. If I flip to the small peep, I'll be about zeroed and won't be 2" low until about 250y.

But anyway, that is not the point of your thread.

You say you have a regular A2 flip aperture with no elevation wheel. When you raise the BUIS, it comes up with the larger ghost ring in place. OK, I have the same setup on my carbines with ARMS #40s.

Option #1 You can zero the large aperture at whatever you wish your battle zero to be (aka: PBR or Point Blank Range). A 200m or 200y zero is usually recommended, but that's your choice. When you flip to the small peep, you will have a zero at some longer range. You'll have to test it to see what that is. It will vary from one sight to another (see XS FAQ above). Shooting a group at 100y with the small peep and plugging your result in a ballistic calculator should give you an answer.

Option #2 The way I do it is zero my longer range peep at my favorite PBR and accept that the larger ghost ring will not be zero'ed the same. In my experience it does shoot lower. At under 100y, being off an inch or three isn't going to matter that much. At longer range, your error expands in a cone shape. If I do my part, the smaller peep and known zero gives me a higher probability of an accurate hit at longer ranges.

That is the only two choices you have unless you get the same plane aperture.

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