Years ago when I built my first scratch built trade gun, and a little later my sons miniature trade gun, I got some flat ribbed material to make the pipes from TOTW. It was obviously ribbed by running it through some sort of roller that pressed the ribs into the brass strips. The recesses between the raised ribs had fine ridges that no doubt were from whatever was engineered to give the roller enough traction to make it feed properly.
Hungry Horse