Mike, I think the majority of the BL series guns were marked as sweep describes w/both bbl length & chokes printed on the bbl. However I have also seen the markings individually stamped on the bbls. in mm's, under the forearm. There will be two diameters stamped on each bbl. the larger being the nominal bore dia. & the smaller being the constriction or choke dia. The dif. expressed in tenths of a millimeter you may multiply by 4 [not exact, but more than close enough] to get the constriction expressed in 'points' or thousandths of an inch. Some bbls are marked with the 'star' system; one star = full choke,two stars = more open, &c. If you think there is any chance of the chokes not being original then you want to measure them and disregard the choke markings.
The best method is to simply spend a bit of time shootng some patterns w/the ammunition you intend to use and at the distances you think are most appropriate to the intended game, be it clay targets or feathered. Then you will know exactly what the gun is doing w/that ammunition at the range(s) tested. It can prove a good confidence builder having that knowledge & is much more useful than only knowing the 'choke' since much modern ammuniton actually delivers pattern %'s above what the choke marking would indicate, or not.
kind regards, tw
