It is quite true that PHs (professional hunters, who guide clients to African big game) carry their rifles muzzle forward, hand on the barrel (or barrels, if they have a double rifle, which few of them do). I’ve never seem them carry any other way, except for in the hand, or at what the Army calls “port arms,” when fun is imminent. They do this partly because of tradition. When they began hunting, probably as children, this is how the adults from whom they learned carried their rifles, and tradition is a very powerful thing. Tradition is why you see Austrian and German hunters carry their Drillings slung broken open, beneath their arms.