The gun was originally proofed as a 13 bore, .700”, and the most recent reproof puts it at .728. It may not have had any choke as a 13 bore, but, there was room for it to be jug choked in between that, and the bores finding themselves out to .728, around 100 years later. I’m no expert, but, it appears the gun has had two trips back to the proof house, with contemporary proof at 850 bar, and a previous reproof stamp applied earlier.

Just a guess, but, I’ve seen it before.

Best,
Ted