There is actually a bit of a story there. When Iver Johnson went to their new transfer bar safety device, c. 1894, they decided to use up leftover parts from their old model to make a second quality gun. To keep the IJ name associated with the new revolver, they formed a new company, the U.S. Revolver Co., to market the old-style guns. The line proved popular enough that they not only used up the old parts, but made new guns under the U.S. name.
The U.S. brand was sold almost exclusively through mail order companies.
FWIW, the terms "automatic" and "automatic revolver" applied to guns of that era meant the automatic ejection of empty cases when the gun was opened, as opposed to the manual ejection required of many single action and solid frame revolvers. (S&W designated its swing-cylinder revolvers "hand ejectors" to distinguish them from their line of top break revolvers.)
Jim