View Full Version : Rear Sight Aperture
I noticed that the small aperture on three of my rear sights has a concave surface machined on one side of the aperture. On two of the sights the concave side faces to the rear, Colt A3 and Daniel Defense A1.5. On my fixed Troy it faces forward. Anyone know why the concavity is there in the first place and what benefits if any in the way it faces?
ColtSeavers
11-28-13, 13:29
The concave cutout is supposed to both reduce glare and face the shooter. A LOT of companies get it wrong and put their apertures on backwards (like Troy). No idea why they screw this up as a standard, but they do. I've actually stripped a troy battlesight trying to unscrew the countersunk sight adjustment screw so I could flip the apertures around to face the right way (small aperture at the ready, large aperture to be flipped to) and have since returned it, and moved onto Diamondhead rear flip up sight that I actually like quite a bit more than the traditional aperture sights. The diamondhead also allows you to choose which size aperture you would like left in the ready position without having to unscrew/swap anything around.
+1
In short the concave faces your eye.
Interesting... I had always heard the opposite. The story I'm familiar with was that the original set up was with the "cup" facing away from the shooter. Colt started making some reversed and the industry followed suit.
I actually prefer the Troys because the cup is not facing my eye. I would think the "cup" would stand a better chance of reflecting light into the shooter's eye. In the real world, I suspect it doesn't really mater much either way, and is the kind of minutiae we shoudn't worry over anyway.
As far as function goes, it makes no difference which way it's facing.
HackerF15E
11-29-13, 09:43
The concave cutout is supposed to both reduce glare and face the shooter. A LOT of companies get it wrong and put their apertures on backwards (like Troy). No idea why they screw this up as a standard, but they do.
In short the concave faces your eye.
On every iron-sighted battle rifle I own with a ring rear sight -- Garand, M1903A3, M1 Carbine -- the cutout/cupped/dished part faces away from the eye, and the surface facing the eye is flat. On these rifles (the Garand especially) there is no way to accidentally assemble them backward, so I'm 100% confident this is the way the sight was intentionally designed.
Why would this standard suddenly be different with the advent of the M16/AR-15 style rifle?
Cup faces away. It has to do with focal point and the way light refracts beginning at the point of constriction.
But the difference noted is MINIMAL to almost be non-existent on a field (not target) weapon and even less significant for "imperfect" eyes. Of more significance seems to be the SHAPE of the rear reticle. And interesting article/proposal below :
http://neergaard.org/shootingsight/WHITE%20PAPER%20-%20Rectangular%20Apertures%202011.pdf
Archer1440
11-29-13, 12:51
Cup faces away. It has to do with focal point and the way light refracts beginning at the point of constriction.
But the difference noted is MINIMAL to almost be non-existent on a field (not target) weapon and even less significant for "imperfect" eyes. Of more significance seems to be the SHAPE of the rear reticle. And interesting article/proposal below :
http://neergaard.org/shootingsight/WHITE%20PAPER%20-%20Rectangular%20Apertures%202011.pdf
An article written by the patent holder, who is conveniently ignoring the enormous lateral blurring created with his concept, and the quarter-million man-hours needed to retrofit the rifles in use for the US services alone.
But you're certainly right about it being interesting.
sugerwater
11-29-13, 13:01
I thought it was to reduce the cross section of the sight at the peep area, leaving a larger amount of material for strength elsewhere.
I noted that. He really did a good job of selling his concept. I see it in general use everywhere.....NOT
But it doesn't take away the issue of focal points and the way iron sights work and explains the science of focal points.
Not that his rectangle has anything to do with the concave on normal sights.
ColtSeavers
11-29-13, 13:59
Concave cut out/cup faces towards the shooter. Has been that way on every weapon that had irons that Uncle Sam issued me in the Army.
http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/zero-and-m16a2-rifle.shtml
http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/mechanically-zeroing-the--2.shtml
Concave cut out/cup faces towards the shooter. Has been that way on every weapon that had irons that Uncle Sam issued me in the Army.
http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/zero-and-m16a2-rifle.shtml
http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/mechanically-zeroing-the--2.shtml
Boot.
M-14
M-1 Garand
M-1 Carbine
All three have concave facing forward.
On the A-2 sight it depends on if you have the 0-200 sight (large aperture) up or down.
ColtSeavers
11-29-13, 14:36
Boot.
M-14
M-1 Garand
M-1 Carbine
All three have concave facing forward.
I was never issued any of those weapons and do not own any of them either so I can and have only been commenting on the ones I was issued/do have personal experience with.
On the A-2 sight it depends on if you have the 0-200 sight (large aperture) up or down.
Don't see how that makes any difference other than which aperture you are using. Could you provide a source as I would like to know for my own furthering education?
ETA: I have been referring to the small aperture and it's concave cut out/cup.
Go look at your weapon.
A view from the top at the link:
http://commons.wikimedia.org/wiki/File:M16A2_rear_sight_P1010033.JPG
View from the rear.
http://i158.photobucket.com/albums/t106/chorizo_2007/image-12.jpg (http://s158.photobucket.com/user/chorizo_2007/media/image-12.jpg.html)
ColtSeavers
11-29-13, 15:02
Go look at your weapon.
A view from the top at the link.
View from the rear.
http://i158.photobucket.com/albums/t106/chorizo_2007/image-12.jpg (http://s158.photobucket.com/user/chorizo_2007/media/image-12.jpg.html)
I honestly do/did not remember that. Though, to be fair, I had only ever used the large aperture during BRM in Basic while wearing my Pro(tective) mask and that was only for familiarization of how to shoot while wearing the mask, nothing more. This was at Ft. Leonard Wood back in '01.
HackerF15E
11-29-13, 15:09
So, what we have here is that, with the exception of the small aperture on the A2 and later sights, the concave portion on USGI battle rifles and carbines faces away from the shooter.
I've never thought about how the sight is oriented with respect to the concave. Good thread. visible light going through an opening larger than its wavelength-Huygens' Principle.
clschicago
11-29-13, 20:23
i will say this, i have a hard time seeing through the smaller aperture due to the cup and its amazing ability to reflect ALL of the suns rays right into my eyes. that and it holds water like no other, cant count how many times i have had to blow it off so i could see through the thing.
Failure2Stop
11-29-13, 20:35
The cup really should face away from the shooter.
Very simple reason:
When light from behind the shooter hits the cup it distorts the image that the shooter sees, making the aperture appear to be larger/oblong, making placement of the front sight in the aperture incorrect, causing POI to shift.
A flat sight will uniformly illuminate, permitting POI to remain consistent.
Sent from my VS980 4G using Tapatalk
ColtSeavers
11-29-13, 22:50
I've never had an issue with light ever reflecting back at me/into my eye from the concave cut out/cup nor do I ever remember the aperture becoming oblong either.
My issue is with the sight itself, or at least in conjunction with the front sight post. Trying to line up the center flat point of a W within an O just never made sense to me (though I can do it). It's why I switched out the front sight post for a lollipop type (KNS .052" ball) and that helped alleviate some of the (probably self created?) mental mind block/nagging as centering a small dot inside of a circle is a lot easier for me.
At least until I noticed that the small aperture is backwards and that started a whole new line of nagging that resulted in the aforementioned stripping and return of a Troy Battlesight.
As mentioned before as well though, I have since switched over to the Diamondhead rear sight that makes a hell of a lot more 'sense' to me.
ETA: For full disclosure, I should add that the Diamonhead rear sight also has cut outs on both apertures facing away from the shooter..
I've never had an issue with light ever reflecting back at me/into my eye from the concave cut out/cup nor do I ever remember the aperture becoming oblong either.
My issue is with the sight itself, or at least in conjunction with the front sight post. Trying to line up the center flat point of a W within an O just never made sense to me (though I can do it). It's why I switched out the front sight post for a lollipop type (KNS .052" ball) and that helped alleviate some of the (probably self created?) metal mind block/nagging as centering a small dot inside of a circle is a lot easier for me.
At least until I noticed that the small aperture is backwards and that started a whole new line of nagging that resulted in the aforementioned stripping and return of a Troy Battlesight.
As mentioned before as well though, I have since switched over to the Diamondhead rear sight that makes a hell of a lot more 'sense' to me.
The games our minds play with us...........................
ColtSeavers
11-30-13, 09:59
The games our minds play with us...........................
Too true!
Also, I missed this post whn I edited my last one that you quoted, so to be as forthright as possible and add to the mass (mess?) of information, the Diamondhead rear sight that I have now also has cut outs on both apertures facing away from the shooter as well (double checked last night out of curiosity) just as you and others have experienced.
Given your avatar I can see why you are preoccupied with the direction of the sight.
The cup really should face away from the shooter.
Very simple reason:
When light from behind the shooter hits the cup it distorts the image that the shooter sees, making the aperture appear to be larger/oblong, making placement of the front sight in the aperture incorrect, causing POI to shift.
A flat sight will uniformly illuminate, permitting POI to remain consistent.
Sent from my VS980 4G using Tapatalk
True, because of the parabolic shape of the "cup".
Mike Miller
11-30-13, 18:53
Thanks for everyone contributing in this thread, this is well timed. I just received a .030/.040 aperture that I plan on drilling to ~.046 and .070-.075. I'll try installing it reversed, now.
The cup really should face away from the shooter.
Very simple reason:
When light from behind the shooter hits the cup it distorts the image that the shooter sees, making the aperture appear to be larger/oblong, making placement of the front sight in the aperture incorrect, causing POI to shift.
A flat sight will uniformly illuminate, permitting POI to remain consistent.
Sent from my VS980 4G using Tapatalk
This makes sense. The effect is more pronounced on the M1 carbine, but I also noticed the POI shift on my AR's.
Interesting... I had always heard the opposite. The story I'm familiar with was that the original set up was with the "cup" facing away from the shooter. Colt started making some reversed and the industry followed suit.
I actually prefer the Troys because the cup is not facing my eye. I would think the "cup" would stand a better chance of reflecting light into the shooter's eye. In the real world, I suspect it doesn't really mater much either way, and is the kind of minutiae we shoudn't worry over anyway.
Awesome Signature line!
I have to say I've never noticed they differences. I always thought the cup faced the shooter. I have Troy Sights just g
Have not noticed.
I have a KAC 200-600 Micro rear sight. The cup faces my eye, and this sight is clearer to my astigmatic eyes than any other, be it the standard or match A2 rear or Troy BUIS. The aperture is crisp for me. Is it because the cup faces my eye? I don't know, but I have replaced all of the Troy rear sights with KAC, and I shoot tighter groups at 200-400 with the KAC than any other.
My Colt carry handle has the flip over large/small aperture and the cup faces one way on one and the opposite way on the other.
I have a KAC 200-600 Micro rear sight. The cup faces my eye, and this sight is clearer to my astigmatic eyes than any other, be it the standard or match A2 rear or Troy BUIS. The aperture is crisp for me. Is it because the cup faces my eye? I don't know, but I have replaced all of the Troy rear sights with KAC, and I shoot tighter groups at 200-400 with the KAC than any other.
I just googled that rear and it looks to me more like a hooded rear sight (which is better IMO). It's not really the same as the cup on the traditional rear.
It also appears to be hooded on both the shooter side and the muzzle side.
http://farm7.staticflickr.com/6155/6178138971_59c8991192_z.jpg
Awesome Signature line!
I have to say I've never noticed they differences. I always thought the cup faced the shooter. I have Troy Sights just g
Have not noticed.
Thanks! Yea - I can't recall how it was on the M16A1's I started with many years ago. Most AR's now have the cup toward the shooter which is why I tend to buy Troy flip ups.
It is cupped. If that actually makes a difference is irrelevant to me as long as I can see.
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