NWI has made the mistake that basically every fps shooter does when it comes to three-round burst: tapping the mouse button (trigger) causes all three rounds to fire off. This is NOT how most burst mechanisms work on the actual models.
I brought this up in the alpha too, but I see it hasn't been addressed. Given that Insurgency: Sandstorm seems to be making a better effort than most games at replicating the actual workings of the firearms included in the game, I would expect that the devs would go all the way.
Three-round burst is a modified version of automatic fire, not single fire. The trigger must be fully depressed for the duration of the three rounds in order for all three rounds to fire. A good example of this is in the M16 variants which contained 3-round burst (M16A2 and A4). The mechanism is called a Eugene Stoner 3-round burst, which basically consists of a rotating disk which catches the hammer. The disk contains 2 deep groves between 2 sets of 2 shallow grooves. If the trigger is continually depressed, it will cycle through the two shallow grooves and stop on the deeper groove.
This means that merely tapping the trigger will fire off ONE round. If you were to depress the trigger for longer after that, it would fire the remaining TWO rounds and stop.
There are some exceptions to this, notably the AN-94 which fires a two round burst such that the second round is fired before the hammer even cycles back (called hyperburst).
I understand that implementing this in game might give some macro users some cheesing ability (after all you can click a mouse much faster than you can pull a trigger), but this can be compensated for by implementing a short "cool off" between trigger pulls of like 0.5 seconds or something.
Also I know it sounds nit-picky, but we're going for realism here, aren't we? The way three-round burst works in most fps games actually just doesn't make any sense if you look at how firearms actually operate.