I can't recall chamber length but I have seen several 16-bore pigeon guns, both hammer and hammerless.
While we think of pigeon guns as being long-barrelled, I remember a Westley Richards re-barrelled by William Ford with 24 3/4" steel barrels, tightly choked, 2 3/4" chambers, with a hump-back rib. It struck me that this may have been for pigeon competition, making a quikly moving gun but giving the impression of length in the sight picture.
However, it may just be that the customer fancied slde clips on this gun.
