I'd say it's too light and small, hence unbalanced. Because for larger ACs it becomes too beneficial. True, Artemis IV is only 1 ton and gives a +2 bonus, but missiles always hit in clusters not larger than 5. On the other hand, you have only +1 bonus... Still, seems too unfair. I suggest scaling with the mass of the cannon. From the description, it actually should do this anyway. And I agree with Empyrus that that it should not affect jamming. (Though, I think that UACs should be allowed to unjam anyway.)