I'm an old ex-marine, and I originally qualified with an M-14 at Paris Island. To battle sight the rifle, we fired on a 300" range, which gave us our 300 yard "battle sights". Bullet rise at 300" in the trajectory equated with bullet drop at 300 yards. Even with the rifle battle sighted, you need to adjust the sights to be perfect. Ballistic cards will put you close at longer ranges.
I carried a 14 for a year and a half in Southeast Asia, and it never let me down-even once!
If you think about the time line since the 16 became the issue rifle, there'd be darn few folks who ever handled the 14 still in active service. The folks who use them over at SOCOM probably don't train boots. They would have to be in their mid or late fifties.
As desiginated marksman, I'd suggest a basic 4x scope to go with the 14. If you and rifle are in decent shape, you can hit the black at 600 yards all day long. Have someone at home send you some match ammo. Federal 168 grain would be nice.