I feel like the thing that is missing in this is the distinction between firing mode and tactic used in firing.
* Firing Mode: this is an aspect of the weapon itself. You pull the trigger, it fires 1/2/4/lots of rounds. The two round and four round modes are mechanically/electronically limited (through a cam shaft or similar mechanism) that fires exactly that number of rounds. It is controlled by a literal switch on the weapon (although this can be activated electronically via Smartlink).
* Tactic: are you concentrating on a single target or are you spreading your fire among multiple targets.
* Number of times you pull the trigger.
Also, I think that logically the decrease in attack rating is tied to the number of bullets spitting out of the end of the weapon (as the recoil makes it increasingly hard to aim), and the increase in damage is related to the probability that the target will be hit by more than one bullet.
Also, three seconds is a fairly long time in terms of gaining control of the weapon and re-aiming between trigger pulls. The splitting of the dice pool is really a sufficient penalty.
Therefore, I think I would house rule this whole business in the following fashion, as essentially a two dimensional matrix of firing mode and tactic. This is pretty big alteration, YMMV obviously:
Firing Modes:
SS: you fire one round per trigger pull, no change to Attack Rating
SA: you fire two rounds per trigger pull, -2 to Attack Rating
BF: you fire four rounds per trigger pull, - 4 to Attack Rating (with exception for Wide Burst)
FA: you fire as long as the trigger is depressed, -6 to Attack Rating.
Tactical Actions:
Careful Fire: 1 major action. only possible in SS/SA/BF. You target one enemy. Get an increase to damage rating = rounds fired/2 rounded up (+0 for SS, +1 for SA, +2 for BF).
Rapid Fire: 1 Major action and 1 minor action. only possible in SS/SA/BF. You fire twice in quick succession. Split your dice pool evenly into two packets. Assign these packets to either two targets that are close to each other, or a single target. Damage rating increases as with Careful Fire (+0 for SS, +1 for SA, +2 for BF).
Wide Burst: 1 Major action. only possible in BF. You target two enemies that are fairly close to each other with a single trigger pull. This does NOT require a minor action. Attack Rating -2 (instead of -4), Damage Rating +1 against each target. You must split your dice pool evenly between the two targets.
Spray: 1 Major action. only possible in FA. You fill an area with a volume of fire, firing at least 5 and no more than 10 rounds. Divide your dice pool evenly in a number of packets equal to the number of rounds fired. Assign a packet to any target in the area, including more than one packet on the same target. No damage rating change. This does NOT require a minor action.
This is just framework that seems like a logical "refactoring" of the current rules, achieving the roughly the same result but in a logical fashion I can understand. Again YMMV. And like Hulka, I probably should be posting this to the House Rule thread instead of here.