Transformers gun with interchangeable barrels

Yet another "transformers" gun. These robot vehicles/action figures feature hands and body mounts comprising 5mm holes, into which 5mm pegs on accessories are a push fit. This gun was inspired partly by the "nose gun" found elsewhere on Thingiverse. Updated by separating into barrel and gun body, I have in mind to add various optional barrels at some point.

The threaded end of the barrel has a narrow hole - was going to have the inner barrel pass right through but I figured it needed more are