This paper, the second in a series of two, describes medium scale tests on symmetrical, plane (wedge-type) and conical hoppers aimed at determining the critical outlet size preventing the formation of arches or domes during gravitational discharge of bulk materials. The bulk materials used were limestone, gypsum, coal, cement, and taconite, and their flow properties are described in the first paper of the series. The experimentally-determined outlet size is compared with theoretical predictions based on several existing theories of arching. It is shown that all theories overestimate the outlet size by a factor of about 2 to 4, and the results are discussed in the light of flow parameters value and modifications of the theories.