SH Archive 1680: Cannon with Oval Lumen - what is it?

[KD Archive]

This is not the first time I run into sketches of this weird shape of a cannon. The below is allegedly some 1680 "German Cannon with Oval Lumen". Page 442 of the same book has a tiny reference to this shape (they call it carcass) but the info is pretty worthless. I have two questions in reference to this type of cannons:

• What did they fire? As in, what did the rounds look like?
• Do we have any photographs of these cannons?

Source


​

I did find something similar in appearance, but I'm not sure this is the exact same principle one. Though it still produces a lot of questions.

• Three-shot experimental (LOL, right) breech-loading cannon (burst) of Henry VIII, 1540–1543. ​

Source​

Note: This OP was recovered from the Sh.org archive.