Got an TA01NSN ACOG on my M4gery - used too be real good with it out to 400 meters when I used to practice a lot. Now it sits out west, waiting for me to return. Got an MTAC on a Mini 14 for local use - like the optic, lukewarm on the rifle. Would prefer it on a Ruger AR556 . . . but . . .
Some how I knew of the ACOGs early in the 70S or 80? as they advertised in the small ads in the back of Shooting Times or Guns and Ammo and wondered why I have none when was in.
I don't know why they don't design a rudimentary BUIS into all scopes. Really, how hard would it be to add that little bit of extra material to the tube.
Actually, now that I think of it, you could just make some glue on ones designed to attach to different diameter scopes. Could injection molded them for pennies, and could come with a peel and stick adhesive backing.