That is one of the strangest things about that whole series of revolvers. The original bullet diameter was .376" and that is what the Model 1889 was made for. In 1893, the Army specified an inside lubricated bullet of .357" diameter. The Navy apparently continued to use the old outside lubricated cartridges until the supply was exhausted. Yet, Colt didn't modify the barrel inside diameter until the Army contract Model 1903 and the concurrent commercial production, as part of the change to accommodate the .38 Special cartridge.
This explains something I learned, but didn't understand, many years ago - those guns just don't shoot very well, or at least the ones I fired didn't.