If i hit poa at 50yds with my a-2 using the larger aperture, what changes when i flip to the smaller aperture? 1MOA? 16" carbine
                             thanks

Flipping apertures is supposed to be a 2moa change with a 20" barrel.  I say supposed to be because there are a variety of heights they can be found. Go here: [url]http://www.aosights.com/news.html[/url] and read FAQ #10 (near the bottom) it explains the issue and has the figures you seek.

Theoretically if the large aperture is zeroed at 50 yards (a 200M far zero) then the small aperture SHOULD be zeroed for 300M.  This may or may not work depending on which A2 aperture is mounted on your rifle.  And as far as I can tell you can't specify or differetite the different apertures w/o a caliper.

I zeroed a 16" barrel Colt at 50 yards with the A-2 small aperture and found I was shooting 5" low with the large aperture at the same distance. The only cure for this (predictable) bullshit is to can the A-2 aperture and go with the AO same plane aperture.