36" barrels.......almost assuredly a waterfowl gun.

John:
Not positive about ALL 4 Bore meant for dangerous game; I infer from reading Baker that the early 8 & 4 were smooth.
Later on full rifled, & would have to have been if they were to shoot a Fosbery design bullet, conical type slug, or the "exploding shell".....I have gotten to shoot a Bland 4 Bore single that was in fact full rifled. Inspected a 4 Bore double at H&H years ago that was also full rifled.
- Mike

EDIT:
This has got to be the guy
https://forums.pigeonwatch.co.uk/forums/topic/398690-alan-myers/