Eight bore, 8 bore, or 8 gauge (approximately 0.835" or 21.21mm) is an obsolete caliber used commonly in the 19th-century black-powder firearms. It may refer to either rifles or shotguns. It is the size between the larger four bore and the smaller ten bore. In modern times, this size of shotgun shell has a use in cleaning kilns, by blasting away deposits from a distance. This can be done while the kiln is in operation in some instances. Various loadings are in production for different industrial uses.