I ran into an article by Roger Muhre in Missouri Archives "Point Defence Rules for Brilliant Lances". The article can be found in "Index of archive TNE" in "FFS mods".
If you want a multi-target gatling gun. I suggest the following rules by Roger Myhre.
1) The turret must be capable of ignoring at least one difficulty level increment.
2) Turret must have a Flight Computer.
The PD laser can attack more than one target per turn. The maximum number of targets is determined below.
MT= [(FAx +DM)/CM]/10
MT Maximum Targets
FA Number of Focal Arrays
DM Difficulty Number
CM Computer Multiplier
I personally use 6 FAs 1.2 meters diameter surrounding a beam pointer. I know that X-Ray FAs can have as small a diameter of 55cm and still have a range of 10 hexes. For this reason I make my turrets smaller 1-D ton or less. If you prefer the shotgun approach take the number of shots the turret fires in a turn and divide it by the FF+S#1 Rate of Fire Benefits in Space Combat-- Space Combat ROF Shots per 30-minute turn number. This would make it easier to hit a target. You might allow the number of shots, say for example 800 shots, to be divided by 200 to give the turret a chance to hit 4 targets with a -3 difficulty modifier.
I can see where this could be a dangerous concept, I normally drive small 400 ton or less ships with correspondingly small power plants. If you put these turrets on something like a 500K ton battleship with multi-firing, multi-numbered FAs with a huge power reserve it could strip the antennas off its target leaving it deaf and blind. My reason for sticking to 6 FAs and a discharge energy of 3-5mj although a 6 shooter with a DE of 20mj would make a good anti fighter gun.
PS If you like Roger Muhre's ideas about gatling lasers read his article, the article is longer that I could fit in here and it will help make sense of the gatling idea.
Let me know what you come up with, ship building is a passion with me.