The guys I knew way back when were exceptionally good shots because they were exceptionally good hunters.
300 yards, standing, they would drop a Caribou with the first shot 95% of the time. Uphill, downhill, big winds . . . they were great shots. Dinner depended on it
Don't know if the current Rangers has the same amount of practice and skill as the guys back in the 80's.
.303 very suitable but 7.62 is plentiful and I doubt they would mind the change.
Semi auto is up to them. Not like they need to put lots of rounds down range. These guys would stay distant and snipe.