What are the choke markings for your BSS?
A plug gauge is useless for choke measurements unless you are familiar with how a maker choked their guns, Belgian Brownings were always choked tight so a plug gauge will work for them but you have a Japanese Browning which should have Browning choke marks. As Posted, the only true way to determine choke is to measure the difference between the nominal bore and the tightest constriction at the muzzle. note that this doesn't, mean at the end of the muzzle bit could be anywhere from the muzzle back. That's why you need a bore gauge with fingers that you drag through the barrel and it finds the tightest spot. I use a Galazan Pro Bore gauge, cost is a few hundred dollars but it does the measurement correctly and if spending a lot of money for a shotgun or purchasing many, worth the cost.-Dick
