.223s in M16 type rifles have won 1000 yard service rifle matches using 80ish grain bullets.No offense intended but a .223 at a mere 500 yards only has about 200 ft-pds of energy left... sure at 1000 yards it will break paper and wreck havoc on a prairie dog but it is not quite the best choice for long range sniping at human sized targets.
None taken, I agree with your conclusion, that's why the Israelies use(d) the 300 WM. My point is any rifle, although not optimal, is usuable. Don't underestimate their range. Someone posted on a different thread that the 55 grain .223 was really only good out to 300-500 yards, but the .72 grain rounds are good to 600 yards. The 80 grain competition rounds is a hot rod and has an MV in excess of 3000fps. I believe it is a hand load only, and the length is outside of spec.