Somewhere back in the '80s I ran across a gunzine article by a doctor, to the effect that several rapid hits from a full-auto pipsqueak cartridge is very effective. There is some sort of geometric progression of cumulative effect. Sort of a 1,2,4,8 instead of 1,2,3,4 deal. This is the reasoning behind the effectiveness of the Skorpion with its .32 cartridge and the Mac-11 with the .380.
Keep this in mind while thinking about fire discipline and not wasting ammo. I have known several people who were in small-unit field command positions in Vietnam who said that it takes a good deal of training and surviving several firefights to get the average guy to control himself, to not spray and pray and then run dry.
I've fired several magazines through an early M16, and to me the gun was quite controllable. I've not fired one with the three-shot burst setup.
So, just opinion: Seems to me that the three-shot deal would be easily controllable. Seems to me that the cumulative effect would apply.
Art