Re: Aimpoint on an AR w/Front Site
The mount you have is the Aimpoint QRP mount. Aimpoint makes a spacer and longer sscrews that goes in that mount under the body of the sight to raise it so that when you look through your irons the dot will line up centered in the sight (this is referred to as an "absolute cowitness"). Without a spacer the QRP mount usually superimposes the dot on the front sight base when you have a good cheekweld, or in the top third of the sight (defeating the field of view) if you are lined up on the irons.
Other mounts run a little higher so that when you look through the irons the dot will be in the lower third of the sight(referred to as "lower third cowitness), and when you are shooting heads up looking both eyes open through the sight you will be looking over the irons at the target.
And yes, if your rifle/carbine's irons are zeroed you can slap an Aimpoint (or other red dot that co-witnesses) on and use the irons to zero the dot.
If anyone knows where to get a spacer cheap I could use one as well as Artic Light, I just got an M2 with that mount on a trade without the spacer.
Artic Light-you may want to double check that who you got it from doesn't still have the spacer and screws. When issued as the M68 CCO optic by uncle sugar, they come with that mount and spacer (and a goodeneck mount for fixed carry handle A2's).