Thanks a lot guys.
I've not cast it, that is the one & only at the moment.
I bought the cannon some time back, from Casey (Biohunter). I think he said it was a Dragon Studio piece, but I could be wrong.
The arm & mount were cut from some aluminium pieces we use at work for hinges. I just rooted through our scrap aluminium bins & got busy with the hacksaw!
I also used an adjustable cabinet foot coz it's a ball & socket joint that gives nice, tight articulation to the cannon.
The detail pieces are from various broken toys, a couple of parts from an old x-wing fighter, some lego, k-nex........
*SELF EDIT* Just in case there is any confusion, I have absolutely no intention of casting the cannon, but may consider casting the arm & mount, as they are all my own work.