From the 1905 introduction into the late 1920s the only barrel lengths offered were 26- and 28-inch. The 28-inch was standard with the option of 26-inch. From the 1923 Remington Arms Co., Inc. --
Model 11C Trap Grade 1923 catalog.jpeg
About the same time Remington Arms Co., Inc. revised the Model 11 to a cross-bolt safety 1928/9 they added the 30- and 32-inch barrels. From the 1929 catalog over stamped with the 1930 introduction of the 20-gauge Model 11.
1929 Model 11A.jpeg