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?
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.
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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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…