I don't know, but perhaps superior range, penetration, and a bigger bullet. The first Barretts for the Army were for EOD detachments--I don't know the technical details, but those guys are pretty careful about using what works! I have also personally witnessed the difference in hitting an automobile with a Barrett (a short coast to a stop) versus the standard (at that time) M-21 Army sniper weapon (kept rolling until stopped by a Cobra in a significantly more catastrophic manner than was intended). So, bottom line, I'm trusting the guys at the use level to make the decision on what they really need.
Same with machine guns. Why does a police force like SWAT need an M-4, a fully automatic weapon? When was the last time a cop ever needed to fire a bunch of rounds quickly?
Well said about the 338 Lapua. I have a Dakota Longbow that is a tack drive at extreme ranges as it should be.
The thing that really bothers me about the LAPD an other departments these days is that they have M60 GPMG's, M249's , 240G's etc etc ........surgical precision, accountability for every round and background , safety to those innocent folks downrange used to be a priority for law enforcement.
They go after a criminal in my AO with one of those I know who I would shoot to stop the threat to society.