Look up "silouette shooting" of antique rifles...
Even a good sharps can hit a buffulo a 1500 yards...I have it on good authority a semi-auto .50 with a proper scope can be tweaked to 3000 yards by a good shooter...and the group is more like 8 to 12 inches from a bench or bi-pod..not 4 feet
As allways....Your milage may vary.
Sorry, I mistakenly wrote "group" instead of "practical first shot accuracy". Too late at night, I guess.
The Barrett's recoiling barrel might make for large groups, though, and 1.5 MOA might be about right, at that. Might not, too.
Normal loss of zero could give a first shot 90% "circular area probable" of 48 inches at 3,000 yards, or worse, also. It is rare to see a scope hold a zero much better than 1 MOA through motor transport even over a short period in my experience. Maybe they have better scopes and mounts.
So was interested in talking with guys with first hand Barrett experience. Where does the bullet fully stabilize? You single load, right? What changes gave the greatest increase in accuracy? What made you lose it? Do you notice Coriolis effect? That sort of stuff.