This paper presents an experimental investigation of the flow pattern and wall pressure due to the change of the opening discharge diameter in cylindrical silos. The experiments were performed on a metal silo prototype using corn as a granular material. The silo prototype used in the study was built of a metallic cylinder, which can be opened longitudinally allowing the observation of the flow pattern through a plexi-glass wall, and the wall pressure distribution was measured using a special granular pressure transducer. The present study revealed unexpected results to what might be expected through current theoretical knowledge.