Seamless high pressure piping would be the thing to use. Still wouldn’t be too costly for the small quantity needed. I wouldn’t use cheap schedule 40 hardware store pipe for a hand held gun either. For the devices that are buried, of course, it doesn’t matter, they just have to work once.
I have a few 1 FT. long pieces of DOM tubing, I believe it is, 1” I.D., 1/4” wall. Supposed to be about a 1020-1023 equivalent. Not sure if it true, pierced “seamless”, or welded, scarfed and then cold drawn. Based on the finish I’d say the latter.
My son will eventually make a black powder blunderbuss or small cannon. IIRC, he said it would be good to about 18,000 PSI burst.