a revolver is part of the cylinder, and like any other chamber, the throat should be sized so that it is concentric to the chamber and very slightly over the bullet diameter. At the end of the throat, however, things change. First, the throat in a revolver is at least as long as the maximum overall length of the cartridge; if otherwise the cylinder cannot revolve. The next step is the cylinder gap, the space between the cylinder and barrel. This must be wide enough to allow free rotation of the cylinder even when it becomes fouled with powder residue, but not so large that excess gas can be released. The next step is the forcing cone. The forcing cone is where the bullet is guided from the cylinder into the bore of the barrel. It should be concentric with the bore, and deep enough to force the bullet into the bore without significant deformation. Unlike rifles, where the threaded portion of the barrel is in the chamber, revolver barrels threads surround the breech end of the bore, and it is possible that the bore will be compressed when the barrel is screwed into the frame. Cutting a longer forcing cone can relieve this "choke" point, as can lapping of the barrel after it is fitted to the frame. A consistent lockup is important to keep all these parts in line, and revolvers are prone to abuse that can damage these parts, adversely affecting the accuracy and even safety of the revolver. This lockup consists of two parts, the crane to frame lockup, and the cylinder bolt to cylinder lockup. Many swing-out cylinder revolvers only support the cylinder securely at the rear, and flipping the cylinder open and closed can bend the crane and prevent the cylinder from lining up parallel to the bore. The cylinder bolt, which engages the bottom of the cylinder through a slot in the frame, should provide a relatively tight lockup, and not drag the cylinder during rotation or pop loose when the hammer is cocked at a reasonable speed. Fanning a revolver can batter the cylinder bolt and prevent a solid lockup. Harmonics During firing, the chamber pressure rises from atmospheric pressure to, in a typical rifle cartridge, pressures of about within microseconds. This rapid increase in pressure causes the barrel to vibrate at a certain natural frequency, much like a tuning fork. The