The U S Revolver Automatic Hammer was produced by Iver Johnson between 1910 and 1935. There is no published serial number information and the new Iver Johnson Arms Co. does not have any information on older models.
It was produced in 22, 32, and 38 calibers with a 5 or 7 shot cylinder and barrel lengths of 3", 3 1/4" and 5". There were 2 different grips available, the standard grip with U S on the top and optional oversized 2 piece hard rubber grips.
They were sold through the wholesale trade market and were never listed in the Iver Jonson catalogs. The values for your gun are:
excellent-$250, very good-$170, good-$120, fair-$95, poor-$65.
I hope this helps you,