Below is a pic of the cannon on top of the truck's fith wheel (scale of the truck is 1/10 scale of the cannon is 1/84) just to show the scale of the projects I am used to doing.
The first prototype cannon is now complete and painted, I have managed to order some Hematite rod in 8mm to turn the rest of the cannon. Hematite is a nylon type material and is usually black in colour, the colour making it perfect for Canon. Not to mention the fact that it is very easy to turn on the lathe giving a smooth finish with little sanding. I think it is time to find my tungsten lathe tips that I have stashed away in a cupboard in my workshop. The tungsten tips will make turning quite easy as they keep a good edge even on hard steel like tool steel, so the hematite should be no problem at all.