The following was taken directly from the Official Cosmoteer Discord, as Violet asked me to post it on the forums, ALL CREDIT OF THE IDEA GOES TO VIOLET (A.K.A Gustavs-Pet-Neko (FC) , Discord tag: Pet-Neko#7050)
Update: She has a forum account now, it's this one @Violet , go ping her >: D.
This is a feature that:
1 would add another layer of depth without complexity;
2 would also help make things like lasers still be viable.
You can convert the rotational energy into pure directional upon an impact to calculate the relative angle along with the velocity difference, hope this helps you understand what I'm getting it, do call me if you would like to discuss it or have any questions, thank u >.<

Sorry if you can't see it.
Dmg to armour=sinθ •Dmg;
Dmg of reflected shell=cosθ •Dmg;
To calculate the relative angles you can minus the ships vector from that of the shell;
To calculate how a ships spin would effect it's vector at a point in time (definitely check this don't take my word for it) you should take note of the direction of the force and then multiply the radians per second by the distance (Gus will probably give more clarification I think he knows more about this stuff).
Side notes: It would be a good idea to make a cannon shells damage proportional to the magnitude of its vector (it's speed) (you don't need to do implement the armour idea to implement this or visa versa);
If you are to implement the deflection/reflection idea make sure to add a limited to the amount of reflections for obvious reasons.