quick question on barrel markings

[Milton Starr]

My 10 ga bonehill has 12b/12m on the barrel flats and My Edwinson is marked 10b/11m

What do these choke designations mean ? Oh yeah did I mention I got my Edwinson 10 ga Monday after 4 months of layaway its really a beautiful double . Will get some pics of tomorrow .

[Double Trouble]

It's the inside diameter (measured in "gauge") at the bore (B) and at the muzzle (M).
The bore measurement is usually taken at a specific distance from the breech end of the barrels, but I don't recall what it is. So, the 12b/12m is clylinder bore (no ckoke), and the 10b/11m would be approx. 0.025" constriction.