"Care to share the experiences that led you to lose faith in the M2 Carbine?
How well did the Garand work for you in Vietnam?"
Someone detonated a claymore on the head of my column, killing or wounding everyone ahead of me. Then someone jumped up, ran across the trail and disappeared -- we were all shooting carbines and you could see the dust fly from hits.
When he disappeared, I ducked, and there was another boom. Son of a gun if he hadn't jumped up again, and again you could see dust fly from hits. At this point, my carbine had decided to go on strike, and I drew my Colt M357 (you could get away with carrying private weapons in those days.)
The .357 did the job. From then on, I carried an M1 -- and it worked great. One wonderful thinb about it was, it will penetrate. You can shoot through brush with it -- not straight, but you don't need to shoot straight as you do in hunting, you just need to keep rounds going into the same area.
Let me address another issue:
"I'll defer to people who actually served as machine gunners, but I think the issue is not how fast you shoot up your ammo, but how accurately you can place the rounds while doing so."
IF you are accurately placing rounds in a target area, then you are being effective. Since you can do that as well with an M16A2 as with a SAW, why do you need full auto fire, especially from a heavier weapon?
Now, I fully admit that as a company commander (on my second tour), I used to fine troops $50 for firing the M16 full auto.
I used to take my NCOs into the brush and put out C-ration boxes as targets, siting them as if they were putting men in position. Then we'd go back to the "friendly position" and put up limiting poles.
Lying flat on the ground in in firing position, we'd adjust two tapes -- one near the ground, the other higher. These tapes mark the upper and lower limits -- no enemy can possibly be below the lower one, nor above the higher one.
(Just for an experiment, try that with an iron-sighted rifle -- typically, if you mark the place on the ground where no enemy can be, then the upper limit, they're separated by about three front-sight heights.)
We then brought up the troops -- who had not seen the targets placed -- and coached them. The idea is to fire methodically into the "box." If a squad-sized unit is used, split the box in half vertically -- one team taking the right side, the other taking the left. Leave overlap and stress that to the troops.
Ensure that the troops shoot LOW -- you want to see bullets hit short now and then -- ricochets can be effective, but rounds going over the enemy's head are not.
This can be enhanced by putting claymore blasting caps on some of the targets -- when the cap goes off, the troops have a clue where the target is and concentrate fire on it.
Well-controlled semi-automatic fire like this, from well-trained troops is DEADLY. And you can sustain it a lot longer than you can spray-and-pray.