3 sets of marks.
The oldest are the 21 marks on each barrel pre 1887. A 20 gauge with slightly undersized bores. Barrels might say "not for ball" if either barrel was originally choked. Those marks would be further out on the bottom of the barrels and are not in the photo. I would also expect the other original marks are out on the barrels as well.
The it looks like a mid-life reproof denoting 2 1/2".
Finally a recent reproof to 70mm with metric 15.7/15.9 for bore diameters.
The pre-1887 21 bore marks would be consistant with the period when Jones under-levers were fairly common.
Joe
