So what I've got so far is the 5" twin mount is under guns_radars, the sim file lists it as having 250 AP rounds and 250 AA rounds. Compared to the 16" triple mount which has 300 AP rounds. This brings us to rate of fire (per the game files), 5" is 2(salvo) rounds every 2.5 seconds and 16" is 3(salvo) rounds every 30 seconds. So in a little over 5 minutes of sustained fire the 5" mounts will run dry and 50 minutes the 16" mounts will run out.
So if we want to equal this out (assuming we leave the 16" alone) we need to adjust reload time to around 30 secs, or increase the magazine to 2500 rounds.
Now to test the hypothesis!