Cylinder has .357" diameter throat. Kirst Cartridge Konverter with color case hardened Konverter ring and loading gate to convert 36 caliber Pietta 1861 and 1851 Colt Navy revolvers to shoot 38 Long Colt ammunition. This has been done because it is more convenient to load and unload cartridges without having to remove the barrel to access the cylinder. This does make it necessary that you, the owner, cut a loading groove in the right side recoil shield of your revolver and install the provided loading gate. This is not a difficult task with a few common tools. Simple, step-by-step instructions and a loading port template are included. All Kirst Cartridge Konverters are precision CNC machined in the USA from 4140 Steel and heat-treated. The cylinders are rated "For Black Powder Loads", which includes the current Cowboy smokeless powder loads on the market. No F.F.L. required, S.A.S.S. legal and lifetime manufacturer warranty .45 caliber cylinders must NEVER be installed in a .36 caliber revolver. Not recommended for original antique Colt Revolver or brass framed revolvers. Complete your revolver conversion process by adding an ejector assembly.