I have a page that I had not really noticed. This is from the information about Amsterdam Directors' ships. There is a list of 12pdr guns, some of which are klokwijs (chambered) and some which are normal guns. These are the weights of the six bronze pieces:
Nr. 1 2540 lbs straight
Nr. 2 2560 lbs
Nr. 3 1565 lbs klokwijs
Nr. 4 1505 lbs
Nr. 5 1403 lbs
Nr. 6 1400 lbs