The barrel is attached by two screws that fit into what you call the alloy block. It is basically a metal rail on which the barrel sits. This rail is part of the action, which itself is attached to the stock by a rather large screw that is accessible from the stock end (as well as by the two said screws once they have engaged the barrel as there is wood between the rail and the points where the screws engage). You should keep in mind that the barrel is not just a barrel, it contains the chamber as well. The bolt-head also engages directly in the barrel, which is fairly standard with many modern European rifles nowadays.