Start with the two halves of the central pin.
Slot them together as shown.
One at a time, left to right, slot each of these pieces onto the central pin from the previous step, putting slue in-between the layers, until you make something that looks like the image below.
Lastly, glue the front plate and barrels onto the front of the turret.
You are finished. Prime with Rust-o-leum Profesional Enamel flat black and paint as normal with hobby paints.