Its a 5m long 75mm bore hybrid utilising a class 150 4 bolt flange as a burst dics holder.
the chamber is a 20litre ex-oxygen bottle, and has a single spark plug and a single fill port, I dont currently have any close up pics.
the gun holder is currently temporary and as I get around to it Ill build a nicer setup (tilt and pan)
well here is a pic of the beast

and here is a vid of it as well

Im currently having to rethink my projectile choice, I was firing tin cans filed with concrete, but they seem to be getting the concrete crushed/broken up before it leaves the barrel, Im going to give shaped pykrete a go when I get the chance