Don-the only Pigeon Grade(?) M12 Heavy Duck I have seen was one of the "Fubared 50's" series with the "Dog Leg" slide- a real mistake my WRA- Both Madis and Riffle detail that in their books. Have you ever seen a M12 12 ga. refitted by the factory to 3" and with a verifying letter? I have. But as the M12 HD had a much heavier WT WPS barrel-and the receiver was about .0625" thicker, I wonder how they would hold up with the 3" loads? Any ideas?? I have a friend with two std. grade M21's mfg 1948-1051 era- the 1948 has 30" barrels imp. cyl. right and imp. mod. left, and is marked 3" chamber on the left barrel breech at the 9 o'clock position- the 1951 is a Duck Model 21- 32" solid rib and is choked mod. and imp. mod- with 3" chambers- both have SST and SAE--the Duck Model has a greater wall thickness as measured with a digital vernier caliper both at the breech and at the muzzle-both barrels-did Winchester use a heavier set of barrels for the M21 Duck than for the std. M21 12 bore??

"The field is the touchstone of the man"..