Yes Parker & as I recall some other makers as well intentionally cut their 2 3/4" 12 ga chambers 1/8" short. This was initially done as I recall at the request of trap shooters so may have only applied to the 12ga, not sure.
Until fairly recent times SAAMI specs for the 12 gauge 2 3/4" chamber called for a length to the cone of 2.617" (a bit shy of 2 5/8") with diameter of .698" with 5° cone. At the full 2.750" length this would give a diameter in the cone of .686"or still .057" larger than a .629" bore.
With the minimum chamber of .698 with 5° cone to a .629" bore gives a cone length of .394".
Be sure you have a normal cone, not one of the seldom encountered "Step" chambers, make certain the load inside the shell is compatible with the gun's proof & then don't worry about an 1/8" of hull length.
