There are quite a few rifle builders/custom gunsmiths that make custom riflebbls of all sorts of special shapes and added features( sight ribs, sight ramps, scope mount bases, full length ribs, secondary recoil lugs, etc..all being cut from the same large dia blank to start from.
The bbl profile can be anything you want. Round, round/oct, full oct, tapered.
Nothing added on, attached with screws or solder. All one piece.



It's nothing new, it's been done since forever in the gun building world. But modern CNC equipment makes it an easier chore and repeatable.

Remington used to make the bbls of their Vent Rib shot guns all in one piece.
The old Model 10, 17, 11 and 31..those Vent rib barrels are made as one piece.
The bbl, the vent rib posts and the rib itself are all machined from one solid piece of steel. No separate parts assembled and soldered together.
Pretty good for early to mid 20th century factory work., and on a simple assembly line production gun as well.