The 19 would be the bore diameter ahead of the chamber, the chamber would be identified by a 20 in a circle( if 2 1/2") or 20/70(if 2 3/4"), or 20/76 (if 3 " chamber). For a 1936 Gun it is likely 2 1/2".
Mike

Last edited by Der Ami; 04/30/18 06:33 PM.