6° is so little.
Here it’s like 18° per rotation. Which you would expect from such a mount.
What I found is this:
(1) 40-MM GUN CARRIAGES M2 AND M2A1. The two carriages have different gear ratios in the hand traversing mechanisms. The gear ratio of the hand traversing mechanism of the 40-mm Gun Carriage M2A1 is approximately three times as high as that of the 40-mm Gun Carriage M2. The rate of traverse per turn of the crank of the M2A1 Carriage is 17 1/7 degrees; of the M2 Carriage, 6 degrees. The principal differences between the hand traversing mechanisms of the two carriages are a larger hand traversing mechanism gear case and long and short traversing mechanism bevel gears of higher ratio on the M2A1 Carriage.
So it seems to be correct. Early version had just a 6° turn rate, later it was almost 18°.
So 21°/s is actually pretty generous.
Three times higher traverse is such a night and day difference. It’s crazy that they even built something with such a low traverse rate.
But I guess you can move a lot more weight around with a lower gear ratio, so in some instances it might be handy.