Linkage
The funny thing is, this weapon, when used properly, just straight melts people...
I hardly care how much exact damage it does...
In either event, you need a denominator, and to me the most logical denominator other then time, would be ammo.
1 link ammo expended in shaft, unlinked does 9 damage. Most stat counters take one ammo for a hit, and so if comp calls 1 sound to 1 hit to 1 ammo, then you have your answer, 9 damage a plink.
1 linker, and it does 13 per plink, which fits the previously stated factor of 1.5.
(1+1.5 x 1) 9 = 22.5 ~ 23. 1 link.
(1+1.5 x 2) 9 = 34.0 = 34. 2 links.
(1+1.5 x 3) 9 = 49.5 ~ 50. 3 links.
(1+1.5 x 4) 9 = 63.0 = 63. 4 links.
Which one is most efficient, would be dictated by how ammo is expended.
If per hit, each linker, and the shaft weilder expend 1 ammo each, then it would be more efficient, in the odd numbered groups, starting at 1. Naturally, with multiple people aiming, their individual accuracy facotrs in, and if one can't hit anything with it, and the other can, then the answer changes.
Bolts are a bit different IIRC, in my testing, they do 30, 60, and 90, which makes little difference how you split the linkage. Oddly enough, I can't confirm this, because these hacking bots will only link me if I shaft...