My 1938 NID 3.5" measures .750" in each barrel and each measures .038" of choke. Last time I patterned it over 40 years ago, It was 90% at 40 yards in a 30" circle with 2 1/8 oz of nickel plated BB's. Right barrel was 55% at 40 yards with a spreader load of 2.5 oz. of #3 chilled lead (St. Louis Threes). The loads were for spring gobblers. Gil