Comment Re:Lock, stock and (Score 1) 443
It depends on the gun.
For pistol cartridges, you can actually get away with a smoothbore barrel made out of standard steel tubing - this is how Luty's SMG works. It's not going to be accurate, of course - but within 50 yards, with a full auto gun, it hardly matters.
For rifles, the DIY gun community has figured out a way to use electro-chemical etching to make rifled barrels without the usual tooling.