It is interesting, could it be that in the old days the barrels where not just "choked" the last 2 or 3 inches of barrel. What is the measurement from the chamber down say half way. Like I said I'm no expert in this arena. Just to add some info., I have a German shotgun (circa 1920) marked full choke and you can see 2 steps looking down the 26 inch barrel, one half way and then another about 4 inches from the muzzle. Things weren't always done in the past as they are to-day, Perhaps someone more knowledgeable will chime in and explain the use of 11 / 12 on on 10 gau. --- John Can.