I have one of the "older" service grade m1A's and I mounted a Hawke 30 tactical using a sadlak mount. I get the best of both worlds. I use the iron sites to zero the scope at 100 or 200 yds and I can switch to the scope. I'm not the best shot in the world but I generally get 2~3" at 400yds with the scope and about 4~5" with the irons
I also shoot an AR10B (sudan version) that I shoot with the iron sights only. It's not as accurate as the m1a, probably because of the shorter barrel. I'm satisfied with both.
Both rifles use the same varget load, 39.9gns and 168gn BTHP bullets.