I have the benefit of having been in for a pretty good amount of time. I served from 1981 to 2009 (28 tears) so I was around for both the full auto times (M16A1) and the 3 round burst times. (M16A2/M4) I was also an Infantry Drill Sgt at Ft Benning, GA who spent a lot of time on the range teaching the IET (Initial Entry Training) soldier BRM, (Basic Rifle Marksmanship) and at the end of the day, (to expend unused ammo) and often to demonstrate the ease of controllability, we would spend extensive time utilizing FA fire with the M16A1.
What so many people fail to realize is that FA fire isn't there to hit targets. At least not when utilized in a basic issue infantry weapon. That role is reserved for the machine gunners. While it can be used in that role on a limited basis, it's primary design is in giving the capability to the individual soldier to extricate himself out of a sticky situation, or to allow himself to advance towards the enemy under that fire to further the mission. (it's a scary noise maker, like a machine gun) Being light weight (no heavy barrel, or means of a quick change barrel) and still being magazine fed (limited ammo supply) a FA fire basic issue weapon isn't designed to have the FA fire in use long term. It's an emergency use option. One to be sparingly used, as the need arises. If you need to keep an enemies head down for a few seconds to move to cover, or to cover your team member so they can move. If you are overwhelmed, and need to break contact. If you happen upon a target of opportunity, say of a mass of troops up close. (maybe you're point man, or tail end Charlie on dismounted patrol) Unfortunately, this requires training, and discipline, something the Army started laxing off on right about the time of the development of the M16.
As far as it being a waste of ammo... yes, it can be, if used improperly, or with undisciplined troops. However, the myth of it being ineffective, or incontrollable, is just that... a myth. Especially with the M16 platform. Even when I was a 17 year old 136 pound pvt, I learned to easily control my m16A1 with both semi-auto, and full-auto fire. The design of the weapon, and the low recoil of the round, make for very easy to control weapon, even in FA fire. As far as the 3 round burst mode goes, that's a crutch solely to limit troops... used as a band aid due to poor discipline. It's not as accurate as semi -auto for a well placed shot, and not as effective at suppressive fire when needing to move, cover your teammate's movement, or break contact. Furthermore, with the selector on Auto, it's very easy to get three round bursts (or thereabouts) with training. FA fire isn't a capability you need all that often, but it's one that when you do need... you need it, and not a weak 3 round substitute of it. I'm pretty sure the only reason it was done away with was because of training shortcomings. It was those shortcomings, that lead to the wasting of ammo, NOT the capability of the weapon system.
