Rear Sight Aperture

[3 AE]

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]

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.

[CaliRider]

+1

In short the concave faces your eye.

[El Cid]

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.

[jb1911]

As far as function goes, it makes no difference which way it's facing.

[HackerF15E]

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?

[Chorizo]

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/W...res%202011.pdf

[Archer1440]

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/W...res%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]

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.

[Chorizo]

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.