Klokwijs and regular 12pdr guns

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