Does anyone know if a FSB that uses an A2 post can be converted to an aperture? I heard about a front aperture/rear ring iron sight setup where the human eye can line up concentric circles better than the traditional front post/rear aperture.

Yes it can and many sell the replacement sights in differing styles your referring to.....

Mike

I believe KNS makes a round front sight with a cross hair reticle.  I think it just replaces the front sight post.  Global Tactical sells them.  I'm sure there are others.

Found it: KNS Front Sights

Quoted: I believe KNS makes a round front sight with a cross hair reticle.  I think it just replaces the front sight post.  Global Tactical sells them.  I'm sure there are others. Found it: KNS Front Sights

I have one of those and I like it.  Its not suitable for a SHTF rifle cause mud can easily clog it up and its tough to get out without ruining the crosshairs.  It would be better for taget use if the crosshairs were thinner than they are, but for people/deer sized targets its great for the ranges most can use open sights at.  The front aperature does not seem to make me any quicker though.