the big one is marked 'FOR SUPER SPEED & SUPER-X 3IN', the 28 is marked MODEL 12-28GA with 2 7/8 CHAM. above and MOD. below ga designation, and 20ga 25" FULL has no chamber length stamped on the barrel.
i gather the real ole' winchesters don't usually have chamber markings on them.
ole mod 1897s & mod 12s in 12ga are easy because i don't think anything shorter then 2&3/4 acually exists. i does not mean much but i have never seen short-chambered mod 12 12ga.
i like to add ole' '97 to my vault, but everything i see around here has zero blue and looks terribly worn. i am told that's becuase these were fav guns of ole' market and for the pot great depression era hunters.
