Looking @ the #40 am I safe in assuming that all elevation adj. are done @the front sight. What are your prefrences in a BUIS ? ARMS, GG&G, BM, DPMS...?

               ........Paul

You're correct, the elevation is adjusted via the front sight post.

The ARMS #40 is by far the best flip-up style BUIS availble at this time.  I know most of the people on this site will agree with this.

I have the ARMS #40A which has the full A2 small aperture, without the horizon cut.  IMHO the horizon cut makes the small aperture almost impossible to use and the sight is mounted too close to the eye to properly use the long range notch.

That being said there may be exceptions and another BUIS may suit you better depending on the purpose of your rifle and how it's configured.

HTH!

Knight's 300 or 600m flip up rear is a very good BUIS as well, and extremely low profile.