You can do it with ERC, too. No need for any parent child relationship. You turn the elevating screw on the cannon I have in Freestuff and not only does the screw unthread out of the carrage properly, the tube tilts AND the sight rotates to match the tube's elevation (like a proper sight should). No parent/children at all, super trick, what? (ERC is the "master" name for all the Joint controled stuff, in this case the screws rotation also does Y trans for the same part, plus rotation for two other parts. Wasn't super-hard to setup, you can download the Napoleon to see the details in the CR2)