Electric discharge machining and Electro-Chemical Machining are within the range of a the home shop. I was curious and built an EDM borer once (I also built a wire EDM). I'm pretty sure pistol barrels can be bored with rifling in-situ using EDM under distilled de-ionized water. You will need a controller, which you can build for yourself. ECM is also quite feasible these days. Both are tech you can fabricate at home from ordinary materials.
Understood, but I am saying a good conventional home machinist with fairly primitive tools is also able to produce good quality barrels.