I love this thread.
I should go take pictures of a CA legal single shot shoulder fired slambang 12 gauge shotgun. 3/4 inch pipe for barrel, 24 inches long, 3 inch long 1" diameter pipe with the weld seam inside grinded out, 1" endcap, 1" T junction, reducer to 3/4", then some 90 degree angles and an end cap to make a U-shaped 3/4" pipe for the shoulder stock and rear grip. Front grip is the barrel, to fire and make sure it doesn't go flying.