Putting the serial number on the barrel and regulating that makes far more sense,
Not really. Barrels are consumables. They need occasional replacement.
you canâ(TM)t even rifle the barrel properly without specialized equipment thatâ(TM)s not run of the mill CNC.
I've seen some rifling jigs made from all-thread, bolts and an angle iron frame. The trick is just to pull the rifling button through a piece of bored rod. Homemade buttons made from hardened tool steel will do for a production run in the dozens of parts. Carbide is only needed for actual commercial production runs.
And then there are home made EDM machines.