Interesting, the BUIS illustrated is our (KAC) 300 Meter Rear Folding Sight.
Great read and great resource.  Thanks for the link.

Personaly CB I think the KAC 300 mtr BUIS is the best one for an Infantry soldier. Simple but bomb proof. That makes or brakes anything uncle sugar offers its troops. Your product is still the one others are measured by.

K.I.S.S. will always apply where ever durability and longevity counts.

Ar15.com does not favor any particular product over others and my comments are my expressed opinion.

I like them too, regardless for whom I work for.  Others do as well as Crane just bought some more for USSOCOM SOPMOD Kits.  Only problem with these sights that persists is loosing the plastic aperture.  For example, I sent 500 aperture replacements to a unit in Iraq last week.  I adivsed these guys to "string" their aperures on a pipe cleaner when they were removed so they weren't lost so easily.
I have also shot some pretty respectable groups using a second 300 meter flip up on the end of the RAS by just lining up the front & rear apertures on the target the way we were taught with the MP5/HK33's.

I always assumed the primary use of the KAC 300 meter sight was with the larger appearature and the insert was something a little extra above and beyond the core requirements, like icing on the cake.

I have not measured the thickness and clearance, however, would be nice if a second hole in the base could be made to "snap" the insert in when the insert is not being used (or even to carry an extra one).

I agree.  However,I think what happens is that the smaller/replaceable aperture is desired for zeroing, then it is removed.  So there needs to be a way to keep track of this small piece for the next guy issued the weapon can start out fresh.

Had not though of the qualification issue (one of the reasons for the 500 pack maybe ... new wave of qualification / replaments).

Close friend of ours is just finishing up most of a year in the Gulf (got there early and was able to listen to the the Presidents first talk on a little $15 radio that we included in a box from home along with socks, wipes, spices and food) he always indicate "if it was not tied down you would loose it in the field".

Noticed on the photos sent back that they are using one of the Aimpoints with out any BUIS, be interesting talking to him when he is back to know how many times he wished that he had something (then again knowning him ... he might have had another option that I did not see in the photo).