My 1924 Ideal grade 16ga indeed measures .650 in the bore and has .020 constriction in the right barrel and .030 in the left. The chambers measured 2 5/8 by my gunsmith and I use 2 5/8 shells in it. I cut all my hulls to that length while the Fiocchi hulls that I have seen and Agila hulls as well measure 67mm or 2 5/8" The Remington game load hulls used to measure that but some new ones that i picked up recently were the full 2 3/4