One of the "neat" things about the Parrot Rifle was the way it was made:

The tube and breech re-enforcement band were separate castings. The tube was machined on the OUTSIDE while the re-enforcing band was machined on the INSIDE. The whole point of the mahining was so that the Interior Diameter of the re-enforcing band was slightly SMALLER in diameter than that of the rear of the tube.

Then the re-enforcing band was heated to almost a white hot (the hot metal expanded) and slipped over the rear of the cool tube. When the re-enforcing band cooled is was solidly "locked" on to the rear of the tube. Then the "Touch-hole" was drilled thru to the interior of the bore.

You gotta admit, that is a unique way to make a cannon.