I finally have the $$$ for an Aimpoint and BUIS for my Colt M-4.  I'm sure this topic has been beat to death, but how do I co witness the iron sights and the optics?  Do I simply sight in the iron sights and  then once sighted in, bolt on the optics and adjust the dot to be right on top of the front iron sight?  Do I need to play with the mounts in some way or get the proper height mount?    

Sorry for such a "simple" question.  Thanks for any help.  

basically yes, get either the larue tall or cantilever mount and it would be the proper height to cw.


there is also the arms mount which you will need either the tall or cantilever spacer.

Need to check the zero on your iron sights with the optics in place - can in theory be a slight shift.

I just got a La Rue LT 150 mount and an Aimpoint M3 and it cowitnesses perfectly in the lower portion of the Aimpoint sight. It looks exactly like it does in this illustration (Lower third example):





So basically if I want to use my BUIS, I just lower my eye a little bit and viola, instant cowitness.