It's possible... there are quite a few standard copper pipe sizes that
come out to 50 ohms.

I think supporting dielectric disks or whatever are the hard part in
rolling your own. We did actually build a small section of 50 ohm
hardline for a sodium droplet pinch-off experiment here... I think it
was 1/2" pipe inside 1 1/2" pipe.

If you were trying to do a long run of it, though, you'd quickly get
into assembly hell. #10 wire inside 1/4" refrigeration tubing comes
out awfully close to 37 ohms; tried to make a matching section for a
440 MHz yagi this way, but I couldn't figure out how to keep it
centered, so it never worked out.

Dan

Jeff wrote:
There is an apocryphal story that 50 ohms started out as a common impedance
for coax because that happened to be the number that came out using common
British copper pipe sizes.

73
Jeff