Evergreen makes styrene tubing suitable for use as cylinder chambers in the old Pyro SAA Colt .45.
Not certain about how well other tubes will work for different calibers.
I suppose that may not matter if the builder doesn't have access to actual ammunition or "Snap Caps" to check fit.
As for lack of plastic model kits, there are ways around that limitation.
For the last couple of years, someone has entered carved wooden pistol replicas in the Chicago MMSi contests.
Very nicely done, as well.
Of course, the builder needs access to decent photos or drawings of the original.
Also, there are paper model kits of military assault rifles and even an RPG available for download.
I view the main benefit of the full scale plastic gun replicas as being that of learning tools.
The 1970s era Japanese LS series plastic models assembled into the same major components found on the actual devices and could be used to teach how each design functioned.
The old 1970s era Collector's Armory pre-assembled zinc metal replicas could also perform the same function as a learning tool.