I see what you mean, but I'm not sure that that is a gun. Anyway, study the object closely, it offers its' own clues.
It almost looks like a huge fire sprinkler (upside down). The "cannon" looks more like some kind of pipe. What is throwing me is the right angle on the chase (unless it is actually a "tee").
Forget about the cannon or any other object in the picture that is not attached to the main object. Look closely at the object, y'all are missing an obvious clue.
Hell idk man. The bolts suggest it's some sort of press, and what are those round things sticking out of the holes? Didn't sound right did it?
Does sound kinda wrong However, those round things sticking out of the holes should be your key. Figure that out and you will figure this object out.