gjk,
I can't say, for sure, that the drilling was made in 1891; but I can say it was made before 1893. In early 1893, it would have been required that it be proofed, and no proof marks are shown in the photos. If it had been completed before May of 1893, but still "in stock" then, it would have a "crown V" stamped on it, in lieu of proofmarks. This means it was not only made before May 1893, it was also sold before then. As to the question of caliber, absent proofmarks the only way to know is through making a chamber cast and "slugging" the barrel. This seems to be a nice old drilling, you are lucky.
Mike.
