These barrels are hammer forged. That process forms the chamber along with the barrel internals as the barrel material is literally hammered into shape over a carbide mandrel. The barrels are then blued and fitted to the action. Then a pull style reamer that contacts the shoulder area of the chamber is used to set the final headspace. That's why only the shoulder area of this chamber appears as a machined finish.
Many other mfgs use the same process of course but blue the barreld actions together after headspace is set...which is why you don't see the shoulder area of the chamber in the 'as machined' finish.
As always, understanding a process can help us make sense of what we see. This one made me go back to basics when I first saw it.
Good shootin' -Al
