Artillery was much faster at this time, especially the prussian.
Well the thing is nobody would be able too keep that rate of fire for a very long time. Like when you read history about the Seven Years' War you hear about the Prussian infantry being able to do 6 volleys a minute. Obviously yes they were able to do this, but only in short bursts because you'd get extremely tired.
Same with artillery in 1870, if you read they were able to fire __ rounds per minute that is usually the high end the crew would be able to do since
A. The crew would get very tired from doing that in an extended amount of time.
B. The barrel could overheat and bend from firing too much.
And probably a few other reasons i cannot think of.
So i don't know, maybe make a cool-off period after firing a lot of rounds? Not even sure if that is possible to make, maybe there is another solution?