If you will note, I asked what the round was. I was assuming 308 since that was the round in discussion but I asked for the round to be indicated so I could be more accurate in my discussion.
Assuming Hathcock was firing standard ball ammo, and assuming a dry air medium, and assuming no negative wind, and assuming an initial muzzle velocity of 2800 ft/sec, his round would have struck his target in almost three seconds while still supersonic. His accuracy would not have been effected by subsonic drift.
You are correct in that the 50 BMG can be supersonic out to 2500 yards; barely.
But the time would be almost FOUR seconds, not three.
I'll concede that.
My point is, don't think you're the only one on this forum who knows anything about ballistics or the only one who can calculate basic math.