1. Ammunition production menu:
The shells for Leman Russ Battle cannon and Earthshaker Cannon is both labelled as Battle Cannon Shells in the production tab of the Assembler, it only displayes correctly once it is created and added to the inventory.

2. Leman Russ Battle Canon & shells
Cannon have a small grid port but shells can't be loaded via the port or from a small grid Small Cargo container. The shells also can't be moved from one small grid Small Cargo Container of the same size as the port on the back of the cannon to another or via attached conveyors of the same size.

The damage also seem very low, 9-10 shots to destroy a large grid Light Armour block, the vanilla Assault Cannon can destroy such a block with 1-2 shots.

3. Earthshaker Cannon
Can't be reloaded via the small grid port since it can't be selected. Shells can also not be transferred between small grid Small Cargo Container blocks or via small grid Conveyors the same size as the port on the back of the cannon.

Cannon is too heavy for small grid Rotors to rotate up and down. Maybe drop weight down to the same as two vanilla Railgun's combined weight.

4. Lass Cannon
Cannon is too heavy for small grid Rotors to rotate up and down. Maybe drop weight down to the same as one vanilla Railgun's weight.

5. Nova Cannon
Access port is not accessible, thus can not load ammo into it manually or via large grid Conveyors