- Edited
Welcome back! What is wrong with calling a different shader for the big cannon's built-in shield, as suggested by GunsForGuns? (scroll back to 10 Jan.) It seems to work that way. Edit: ok, I read your other posts and never noticed that the entire part was disabled, when the shield went down.
Separately, why not just balance a big cannon with double hitpoints of the medium? The long range shield is cool, but maybe not necessary. If the gun is buried deep inside a ship, we can cover it with normal shields.