what kind of red dot sight do have on it??? + and Minuse sfor this setup.

Bi level rail for the carrying handle or the bi-level rail on the SIR??

carry handle..

ARMS#39 is an excellent option for your A2 upper. It is build with the Aimpoint and Reflex in mind.  With an Aimpoint, you will require a ARMS #22/m68 and with the Reflex you will need the weaver mount or the ARMS#15.

By selecting a #39 bi-level rail you will not be able to use a duble shield sytle handguard on the top.

thanks, it seems sturdier than the Bennie Cooley mount. You have any idea if a holosight would be compatible??? In regards to the handguard, that was my next question. thnaks. I haven't decided yet.

It is an extremely durable and sturdy.  I have not had any problems of any type with it.  Any sight/optic can be mounted on the mount, but not all will cowitness the iron sights.  To my knowledge, from responses from other members here, there are no "reflex" style optics that will cowitness.  If I remember correctly, the distance from the center of the optic to the mount is 1.5 inches.

Sarge

BTW, you can use one M4 style handguard on the bottom, but the top one has to be the standard style.

I use it with a Eotech and it works great.