From my estimation, ABS is probably better than PVC, since it has thicker walls and the other reasons listed in that website bentioned earlier. Besides, it already comes molded in Tactical Black.
Which reminds me, I will have to post some pics of the EBR spudgun we built about 10 years ago. Tactical black ABS, 24"x3" chamber, 36"x1.5" barrel, custom welded grip assembly with collapsing stock, ventilated barrel shroud (like a Ma Deuce), under-barrel ramrod storage, and a crude "sniper-scope" (PVC pipe with crosshairs).
The neighbor who helped us build it has several in camo ("Jungle Spud Mk I-IV" stenciled on them) one even has a compensated barrel.
The magazine fed version is still in development.
ETA: the bevel is a good idea for properly fitted potatoes, instead of smashing it in with a board, I suggest twisting it in, then using the ram-rod. Be careful not to cut your hands if the bevel is sharp (it will need to be re-sharpened every few hundred rounds).
Also, a better method of shooting "blanks" is to simply cover the muzzle with masking tape, load propelland charge and fire. Makes a really loud BANG!.
Impressive muzzle flash at night.