While, I don't relish the act of questioning the veracity of a brass plaque; paraphrasing what "Willie the Shake" wrote in "Hamlet", 'something is not right in Denmark'. There is a lot of confusion in the writings about and discussion of, the "James Gun", because there are really three different types of cannon that are sometimes referred to by that name. I'm not going to get into that here but the photos that Tim took are of 14-Pounder James Rifled Guns with the characteristic 3.8'' bore. These guns are sometimes referred to as "Type II James Guns" and they echo the outward appearance of John Griffen's 3-Inch Ordnance Rifle. As far as I can tell these guns were first made for Charles T. James by his close friend J. Tyler Ames at the Ames Manufacturing Co. in Chicopee, Massachusetts in 1861; few were produced after 1862.
I thought the twin vents on some large iron guns were for the purpose of extending their working life-spans. I haven't read this in reference to the 13'' mortar but I've seen it in literature about the large bore Dahlgren shell guns. From, Civil War Naval Ordnance by Eugene B. Canfield; "Because the vent became enlarged or eroded more quickly than other parts of the piece, two were arranged in the Dahlgren shell guns. One was filled with zinc, the other being used until it became sufficiently enlarged to endanger the piece. It was then filled with zinc and the second vent bored. Other times the right vent only was bored, the left vent being unbored or partially bored".
That Spanish Howitzer is a beauty. The legend cast into the breech ring is documenting the fact that the gun was cast in Seville on June 16th, 1878. The cypher on the trunnion swell is the royal crest of Alfonso XII, the king of Spain at the time. The lettering cast into the chase that you can see a little of in the photo taken of the chase and muzzle ring is probably the name given to the gun; this being a long held Spanish custom. It would be fascinating to know the provenance of this barrel. I'm going to make an educated guess that it was "reassigned" to American ownership during, or shortly after, the Spanish-American War.
John