Dutch guns from 1653

The amazing thing is that I now have the gun inventories for many Zeeland ships from March 1653. Some guns of greatly varying shot sizes weighed the same. That explains, in part, why some ships might have what seems to be a very heavy armament: the guns carried turn out to be very light, usually chambered in the normal way, or with the bell-shaped chamber that the Dutch called "klokwijs". Some examples:

18pdr half-cartouwen bronze  3200 lbs
12pdr                bronze  3300 lbs
 5pdr                bronze  1750 lbs
 5pdr klokwijs       bronze  1850 lbs
12pdr sakers         iron    3200 lbs