I just took delivery of a new BUIS for my flattop. Not being used to the A2 sight, I was surprised to see the short-range aperture drilled off-center. At first I thought it was a quality control issue, but a quick check of my Guidebook For Marines showed an illustration with the same off-centered aperture. (Screenshots linked below)
                   
www.wzrd.com/~rbrennan/misc/arms40.jpg
                   
www.wzrd.com/~rbrennan/misc/usmc_a2.jpg

My question(s) is/are:

1. Is this common to all A2 sights???

2. Why would the short-range sight be off centered???

(It would seem to me that you would lose the centerline of aim when flipping from the short to long range sight...)

As you flip the sight it is on a screw and that causes the whole aperature to shift to the side when flipping to the small aperature.  Watch it closely and you will see it moving just slighly.  The off center hole counteracts this shift whil rotating on the screw.

Quoted: As you flip the sight it is on a screw and that causes the whole aperature to shift to the side when flipping to the small aperature.  Watch it closely and you will see it moving just slighly.  The off center hole counteracts this shift whil rotating on the screw.

...D'Oh!!!...

So simple...Why didn't I think of that???

Thanks for the explanation!

Excellent question.

Excellent answer.

I learn something each time I visit this site!