I have an LMT 16 incher and was considering an Eotech 512.  What kind of mount if any are you guys using.  Also what kind of BUIS do you use?

Thanks.

I mounted mine directly to the receiver's rail, no mount.  I use a Troy flip up BUIS.

I had the RRA Dominator, great mount with built in A2 style BUIS (similiar if not the same as the LMT or cut carry handle).  But I sold it because I felt I did not need it.  I like it best with the EOTech mounted directly to the upper, the FSP doesn't get in the way for me.

EOTech's come with a built in mount, so I assume you mean what other mounts are used.  

The 2 most popular seem to be the LaRue, which raises the sight slightly so the front sight post sits lower in the window, and the GG&G Accucam which replaces the factory thumb screw with a throwlever.

I use the factory mount, so for a BUIS, I prefer the flip-up type.  I'm using an ARMS #40.  Troy Industries makes a flip up BUIS that seems to be another popular choice here.

Mine are mounted directly to the receivers' rails.  DPMS Mangonel's behind some, a DPMS Standalone rear on another.

One of my son's has his 512 mounted directly on the top rail of a YHM 4 rail forearm, which is the same height at the A3 receiver's rail.