We never used the full auto option on the 14s, at least that I saw. Just too much muzzle climb. The attraction of that weapon for us was that it was 7.62, it ran beautifully in various environments, even when filthy, and it was accurate out to a good 800 yards. When I was at team 1, every man on the team was trained extensively at longer ranges, as well as typical stress course/assault rifle usage. That was a strong shooting bunch. Marksmanship was a critical factor in every single training evolution. It's harder to get that with the 5.56 weapons, even with the improved ammo.
I would have to think that a platoon of Marines in a defensive position, all slung up with their M-14s would be a hard-shooting bunch back in the day. Don't want to sound like a broken record, but I really hated to see our military move away from the 7.62 round. The 6.8 might be the next step back in the right direction, but as I understand it, the political red tape just isn't likely to allow it, no matter how much sense it really makes.
Man bullets for man targets, dammit!