What Is a Cylinder Bore?

A "cylinder bore" refers to a circular tube drilled into a medium, where the diameter of the tube remains constant. Cylindrical bores are found in many products, such as shotguns, musical instruments and engines. In common usage, the term "cylinder bore" most often relates to shotgun barrels.

The cylinder-bore shotgun uses straight pipe; thus the shot, when fired, spreads accordingly. In contrast, shotgun barrels that are not cylindrical are said to be "choked." In a choked barrel, the diameter of the bore does not remain constant, but instead decreases. Shotguns have different styles of choking that yield different shot patterns. Generally, the greater the constriction produced by the choking, the greater the density of the shot pattern. Thus, more choke means more difficulty hitting targets, since the shot pattern will be more constricted. In contrast, no choking, or a cylindrical bore, yields a broad shot pattern; thus targets are easier to contact. The power of a given shot's impact upon a target depends upon the density of the shot pattern. Because of this, while shooters will strike targets more easily when using a cylinder bore, the lessened impact of the shot may not destroy the target. In addition, the degree of shotgun choke determines how far the shot will travel, varying from about 20 to 40 yards.