It is great news that vanilla cannons are added within 1.9, the new part now could facilitate vehicle (and ship) builders as the redundant massive amount of parts are no longer needed. However, there are some issues that causes the cannons to narrowly miss perfection (but still awesome!).

1. The cannons are not able to perform a salvo (all guns shoot simultaneously) if multiple of them are deployed to a vehicle (also, ships). This could be a pain as the only solution (for achieving a salvo) for such condition is go back to the [firingdelay] trimming, which takes nearly the same effort for creating the same effect before the cannon part emerged. And you know, a vessel could have up to 14/16 (main) guns located in different locations, the effort to create the salvo effect would be like that of Sisyphus, endless and not very rewarding.
   Personally, I would suggest to add a switchable property in designer, in the part interface, that could let the player decide the simplest shooting mechanism & logic of the cannons - to salvo (or taking the logic for the miniguns) when the corresponding button has been activated, or to shoot independently like right now, similar to the missiles and rocket pods. This would add a lot of love and fun for the “naval” players (and maybe those who want armored trains).

2. The ballistic property of the cannons, right now, is decided by factors that are too monotonous (pardon me for cannot think about a better word for it) under the same variables. It (may) be a good idea to add shell weight that only affects the ballistic curve.

Still, this update is great, while adding the features above would probably make it even greater. Thank you for taking your time for reading and taking consideration of my personal suggestions.