Probably means that someone in the past extended the chambers. This was not always done very carefully, for example I used to have a Crescent sxs that you could look down the barrels and actually see the difference in chamber lengths (compared to each other). Apparently, they were both supposed to have been rechambered 2-3/4's since that's what the shortest of the two chambers measured.
Steve

Approach life like you do a yellow light - RUN IT! (Gail T.)