Before the Nazis took over- the German and Austrian gun makers, whether building schrottenflinten, bockflinten or drillings- tending to bore the shotgun barrels to the tighter standards prevalent in the European gun making community. One good example of this, albiet with a segue to the "Belgies" are the 12 gauge Belgian mfg. Brownings- both A-5 and Over/Under- where they used a dot-dash and asterik marking to denote full choke, modified, imp. cyl.
American gun makers at that time used a NBD of aprox. .7290" for a 12 bore- no matter the chamber length- European makers tended towards a NBD of .7250"-- and whereas Winchester and Remington used a 0.030" constriction (on a 12 ft. radius/ogive curve) for their full chokes- European makers used anywhere from 0.0335 to 0.040 constriction.
Some of this has changed in post WW2 mfg.'d shotguns- but always not too much- I have a Browning light 12 A-5 made in 1961 in Belgium- 28" VR barrel mod. choke- (by their handbook that came with it) and it patterns AA trap loads as tightly at 40 yards as my M12 Pigeon Grade Trap gun full choke mfg 1948!!
