From a bench, and good supports, I can get as good as 1.6 or so MOA at 100 yards with irons and match ammo (Sierra 53gr BTHP, for example). The same gun will shoot about .9 MOA with a Leupold on it, so that extra .7 MOA of slop is all aiming error on the shooter's part. [:D] It's even harder with a carbine and a fat Trijicon front sight, but my requirements for the irons on those rifles are only 200m.
Using M193-spec ammo, 3 MOA is typical from a bench or prone. With older surplus FMJ, 4-6 MOA is not at all unusual.
Most of the people who talk about "1 MOA groups" aren't testing properly. The proper way to measure groups is NOT to shoot 3 shots and discount the "flier". If you want to know how you and your rifle REALLY shoot, fire 5 strings of 10 shots, and count every shot.
-Troy