A rotary milling system includes a body rotatable about its longitudinal axis and pivotable about a pivot axis that is transverse to the longitudinal axis. The system includes an interchangeable discharge grate and a solid cover for attaching to an open end of the body. The discharge grate includes a plurality of holes through which milled product can pass while grinding media is retained. The body is pivotable to a vertical orientation, where the covers can be changed, and to a horizontal orientation where grinding can be performed with the solid cover attached or discharge can be performed with the discharge grate attached. The discharge grate is sealed to a discharge housing during discharge via an annular seal, where the discharge grate and body are rotated relative to the fixed discharge housing. The discharge grate can include a deflector portion that deflects milled product away from the annular seal.