It is an N-frame 38/44 Outdoorsman revolver. The barrel caliber stamping will be .38 S&W Special, but it was designed to use a somewhat more powerful loading than the factory standard .38 Special cartridge. That cartridge is often called the .38-44. It is no longer made by the larger ammunition companies, but some small boutique manufacturers such as Buffalo Bore and Underwood still make similar loadings. To illustrate, the standard .38 Special load produces a muzzle velocity which is around 800 to 850 ft/sec. The .38-44 load is usually 1100 to 1150 ft/sec. Of course any .38 Special cartridge can be fired in yours without problems. No moon clip is required. Those are generally used only in revolvers chambered for rimless cartridges such as the 9mm or .45 ACP.