The big deal with barrels is there are very few manufacturers, which can be shut down by an oppressive government with little difficulty. No barrel, no gun. Insofar as they can be made at home, quality and production rate are nothing like writing large checks and having truckloads delivered from economically captive producers.
There aren’t “very few” manufactures of barrels.
There are dozens of them, of varying levels of quality.
What isn’t there are abundant sources of barrel quality steel. Seems that the “free trade uber alles” crowd thought that making steel was an icky, dirty industry best outsourced to people in the third world, who wouldn’t know quality steel if it were applied to their faces like a baseball bat.
Want to make a barrel? Get an axle out of a car or truck. They’re made form 4140 steel. This isn’t rocket science. It’s deep hole drilling, followed by reaming to size, and then you get your choice of broach or single-point cutting. The twist can be imparted with a sine bar, as was done on the P&W machines of over 100 years ago.
If Harry Pope did it on a converted lathe, so can you.