I haven a five foot two piece Cold Steel pipe, I’ve never had an issue with it sagging.
Too bad you didn't read your own post you started .http://blowgunforum.com/topic/1098-hello-all-solid-or-two-piece/Bought a four foot two piece blow gun from target zone sports. Nice finish well presented but in my opinion the connecting joint is junk. It is very short so you do not get a lot of support at the adjoining members and it is lose. I wrapped two layers of scotch tape around the tube and it fits tighter but still sags due to the shortness of the union. I am going to glue it together and attempt to let it set up in as straight a line as I can. I am looking at the .625 cold steel heavy duty five footer two piece. Hopefully that joint is better. I hear it is threaded so it must be longer and more stable.