A material reduction machine comprising: (a) a frame; (b) a drum housing mounted to the frame; (c) a drum that is mounted for rotation within the drum housing, said drum comprising: (i) a circumferential wall; (ii) a knife having a leading edge, said knife being mounted on the drum with respect to the circumferential wall so that as the drum rotates, the leading edge of the knife cuts an arc that is concentric with and of a larger diameter than the circumferential wall of the drum; (d) means for rotating the drum within the drum housing; (e) a feed chute for directing material to be reduced into the drum housing; and (f) a discharge chute for directing reduced material away from the drum housing; characterized in that said machine also includes: (g) a plurality of interchangeable belly bands, each of which is adapted to be removably attached to the frame so as to form a portion of the drum housing and to provide an inner surface that forms a belly band arc portion that is concentric with and of a larger diameter than the circumferential wall of the drum, said belly band arc portion being adjacent to a portion of the arc cut by the leading edge of the knife, wherein the plurality of interchangeable belly bands comprises: (i) a first interchangeable belly band having a smooth inner surface; (ii) a second interchangeable belly band having a plurality of flow interrupters spaced along its inner surface. (a) a frame; (b) a drum housing mounted to the frame; (c) a drum that is mounted for rotation within the drum housing, said drum comprising: (i) a circumferential wall; (ii) a knife having a leading edge, said knife being mounted on the drum with respect to the circumferential wall so that as the drum rotates, the leading edge of the knife cuts an arc that is concentric with and of a larger diameter than the circumferential wall of the drum; (i) a circumferential wall; (ii) a knife having a leading edge, said knife being mounted on the drum with respect to the circumferential wall so that as the drum rotates, the leading edge of the knife cuts an arc that is concentric with and of a larger diameter than the circumferential wall of the drum; (d) means for rotating the drum within the drum housing; (e) a feed chute for directing material to be reduced into the drum housing; and (f) a discharge chute for directing reduced material away from the drum housing; characterized in that said machine also includes: (g) a plurality of interchangeable belly bands, each of which is adapted to be removably attached to the frame so as to form a portion of the drum housing and to provide an inner surface that forms a belly band arc portion that is concentric with and of a larger diameter than the circumferential wall of the drum, said belly band arc portion being adjacent to a portion of the arc cut by the leading edge of the knife, wherein the plurality of interchangeable belly bands comprises: (i) a first interchangeable belly band having a smooth inner surface; (ii) a second interchangeable belly band having a plurality of flow interrupters spaced along its inner surface. (i) a first interchangeable belly band having a smooth inner surface; (ii) a second interchangeable belly band having a plurality of flow interrupters spaced along its inner surface.