The Dynamite gun was at a strange point in weapon design. Fuses for shells while not perfect were still capable and explosive charges were extremely capable; however, these explosive were extremely temperamental. The explosive force and initial shock of a standard chemical artillery piece would cause the shell's explosive charge to detonate. This lead people to look for other alternatives as being able to lob exploding death miles away was extremely desirable. This would lead to people looking at compressed air/gases which were used in firearms long before this point. Several versions were created with ship born, field artillery, coastal defense, and mortars being among them. The one seen is the coastal defense version which had a bore of 15 inches. One is at the horizontal while the other is at the gun's maximum elevation of 35 degrees.

The model itself is largely hollow so be careful while printing

I got most of my dimensions from here
https://www.victorianforts.co.uk/art/dynamitegun.htm