The units are computer controlled, so firing rates are determined by need. You need to go and review the workings of the system before you write about what you don't understand.
The firing units are in big boxes and the boxes are configurations of lots of loaded barrels, you just change boxes.
A box 6' X 6' by 8 foot long could hold hundreds of barrels of 40 mm granades, with each barrle loaded with maybe 50 granade rounds. There is no shell, just the round in the barrel. Each round is fired by computer, like an ink jet printer.
I don't have any problem understanding the system. I am curious about how easy you seem to think this would be to use.
Since you seem to know a lot about this please correct me if I am on the wrong track. The "box" you describe would hold how many 40mm grenades? Forty or fifty thousand? The weight will be how many tons? Changing boxes would seem to require major hoisting capacity. At the advertised rate of fire the box would be emptied in about one twentieth of a second. This wouldn't seem to allow time to traverse or change elevation so this isn't even spray and pray. If they get in a fire fight the crew will be pretty busy changing boxes.
How many 155mm rounds will the box hold or will it require a bigger box. I suppose a bigger crane will be required to change this box.