A large round baler includes an expansible baling chamber having an inlet at a forward location thereof and defined in part by a lower run of a flexible, endless component arrangement of an upper conveyor, and by an upper run of a flexible, endless component arrangement of a bottom conveyor. In each of two embodiments, the bottom conveyor includes a moveable roller which operates to selectively deflect the upper run of the bottom conveyor so that it cooperates with a lower run of the upper conveyor so as to define a baling chamber having a cross section conducive to starting a bale core at the beginning of the baling process and moveable to a discharge position for allowing a completed bale to roll onto the ground. In the second embodiment, the upper conveyor also includes a moveable roller that operates to yieldably resist expansion of the lower run of the upper conveyor.