Thanks for the reply......
Down To Business:
I opted for the same caliber weapon as on the resin Baneblade only the turret will house two of them. I chose this instead of increasing the bore of the cannon as to allow for working the two guns inside the turret would be cramped enough without increasing the diameter of the shells which I calculate would be on the order of 16 inches (40,64 cm) on a Baneblade. Guns of a larger caliber begin to take on a comical appearance and stretch credulity.
http://i.imgur.com/jH2xUbU.jpg
I started by cutting rings of 1/2 inch plastic and filing and sanding them to a millimeter wide ring and slipping them on the 7/16 inch barrel I then cut and sanded two muzzle flash suppressors 5/8 inch long by 1/2 inch diameter (13,0 mm).
I wrapped two thin sheets 0.020 inch plastic round the barrel base to thicken the breech end and finally I split a tube of 1/2 inch tubing for the base of the barrel.
http://i.imgur.com/PBvXI02.jpg
All that is now required is the final step of the breech which again will be of 0.020 inch sheet styrene to bring the barrel to it's final thickness.