I'm currently working on making a cosplay prop of a Fallout 4 Laser Rifle. Much of it I'm 3D printing due to easy access and quite frankly a lack of spare time to really handmake much of it. One thing that I'm curious about now is the barrel of the gun itself, a very segment of square tubing with rounded corners, preferably around ~4.5" in width based on how I've modeled the back of the gun so far.
The first thing that came to mind here was some sort of prefab tubing, either like metal ducting or a PVC/plastic pipe. However, these either proved to be prohibitively expensive or nearly nonexistent in the size I needed.
Does anyone have suggestions on where I could get/easily manufacture a square tube like this with rounded corners?