Duplo cannon

[Philippe Hurbain]

Here's the current state of 17178
The next thing to do is close the meshes on 16702 and 16703. Any suggestions?
Can the spring be omitted? If not, then the cannon ball shute (X-shape inside big cylinder) must be elaborated to fit the spring.
Is 494 an ok color for the metal screws?

Doesn't seem we can see the spring from outside, so it can be omitted. I'd rather use 383 for screws.