I've built several spud guns using plastic. Worked great using all sorts of different propellents. Hair spray worked the best. Never got around to trying oxy/acetelyne though. Tried hydrogen once. Put a potatoe right through a Tupper Ware plastic container. :o ;D
Also built an air powered one. They are much cleaner. No propellent residue left. The air powered one used a sprinkler valve just like was shown in the vid.
As was cautioned, plastic pipe can explode. I wouldn't use it in the colder climbs of the northern states in winter. Plastic gets brittle with cold.
I started to build an air powered one out of a piece of 2" dia. copper pipe. Below are some pics of it. Looks like I'll need to finish it now.

This first pic shows the parts. 2" dia copper pipe, connector from 2" to 1/2" pipe, end cap and the 1/2" pipe with a spider to hold the pipe in the center of the 2" pipe.

This one shows the 1/2" pipe with the spider inserted into the 2" pipe.

This one shows the pipe located inside the 2" pipe lamost were it will be solderd in.

And here it is all assembled with a six inch ruler standing next to it.
BTW the copper tubing is type "L" which is a very heavy walled tube.
Now I suppose I need to finish this thing since I've talked about it, right ? ??? :-\ 8)
Regards,
Bernd