Cast iron sure wasn't an ideal cannon material. To make it worse, fairly deep rifling grooves were cut in this piece, causing stress concentrations which certainly contributed. The gun may have done ok as a smoothbore, but we'll never know. Many of the early "fluted shell" experiments ended like this. Mr. Sigourney was the first in the US to build and test them, as far as I know, in the 1850's. When the shells worked, they were often very accurate. Sigourney used shells with two flutes, opposite sides, flutes were maybe an inch high, can't recall, but they were like stubby wings which went nearly the whole length of the shell.