Ok, let's talk Navy tactics.
I'm at a Fleet Command, (COMSECONDFLT) and we handle most of these questions in-house, so maybe I can help.
M-14s are in the inventory and we order new ones all the time. All of the new ones we get are Semi-auto only.
The only time a ship's force is using an M-14 is when NOT out in the open ocean. Our typical littoral defense is a helicopter airborne, and small boats wherever we can use them.
Most destroyers and cruisers now have the GE M134 7.62 minigun, which is infinitely more effective than either an M-60 or M-14. These are used when transiting tight spots, like the Suez canal, or the straits of Gibraltar. We also have .50 cal M-2s on deck, and the occaisonal 20mm cannon.
CIWS can be operated remotely by manual control, and would make any small boat threat totally disappear.
The 5" gun, although a very good weapon, is really designed for open ocean fighting, or NSFS operations (think artillery)
Our best bet, when tied to a pier, is to have a very mobile fight stopper in the hands of as many people as possible. That means M-14s, and small boats with M-60s.
These use the same round (7.62x51mm) which makes good sense. If I'm on watch on any ship anywhere in the world, and the Force Protection Officer gives me a choice of weapon to carry around, I immediately say M-14. Try stopping a truck with a Beretta.
The other thing is, a squid with an M-14 can go anywhere on the ship or pier that he is needed. Not as easy with an M-60. These are better fight stoppers, but not as mobile.
Now, the minigun, M-60, and M-14 all use the same ammo, so why make things difficult for the Ordinance Officer by adding 5.56?
That's why we use them.
Questions?