Jeb, Bill Goforth's book on IJ firearms shows 3 guns marked US REVOLVER CO. Two of them are top-breaks. The first is called: US Revolver Co Automatic Hammer Model 1910-1935. There ar two frame sizes large and small and it was made in calibers .22RF...32 S&W and .38 S&W
The second is called US Revolver Co Automatic Hammerless Model 1910-1935, Again, two frame sizes..large and small with the small being a .32 S&W and the large a .38 S&W
The thrid is called the US Revolver Co Double Action 1911-1935, made in 2 frame sizesd..larege and small....except there is a bit of confusion in that when Bill listed the chamberings...this is what he posted.
Frame size Caliber Cylinder capacity Weight W/ standard bbl OAL w/standard bbl
Small .22RF 7 10 1/2 OZ 6"
MEDIUM .32 S&W 5 12 OZ 6 1/8"
Large .32 S&W Long 6 17 OZ 6 3/4"
Large .38 S&W 5 17 OZ 6 3/4"
That says 3 frame sizes to me,but the text says only 2. The point is that this may affect the parts availabe and the ones that fit. BTW, for those that don't know "Automatic" in this case refers to cartridge case extraction.
In the catalog section of Bill's book, there is a listing for all 3 revolvers....The top-breaks appear to be a neavier framed and barreled gun, while the solid frame appears to be more like a typical blank firing handgun in that the cylinder rod is unprotected and the barrel is thin in appearence. The picture shows an unfluted cylinder
That said, I think your gun..if it is the solid frame model is listed by GPC as: Model 1900 which listes the cals .22,.32 and .38 and the notation reads: Most parts available for all other model Iver Johnson and U.S. Revolvers. nd a statement saying that you must stae caliber and...if possible...include a sketch of the needed parts However...the Illustrated Parts Breakdown shows two hammers and both have FP mounted on them One is for CF and the other RF. There is no FP bushing shown or listed. However, the listing for the Hammerless version show a FP #524310 and a part called: "Firing Pin Nut" .32 and .38 cal. #524370
There is also a IPB and parts list for the OLD MODEL SAFETY HAMMER, .22 and .32 small frame and .38 Large Frame which carries the ID note on US Revolvers. Neither illustrated hammer show a mounted FP. but the parts list shows a FP for a .38 to be #524310A and a Firing Pin Nut to be #524370A. All this has some beatring on your parts search in that there are several such named firearms and that can lead to some confusion when you try to ascertain if the seller has the Exact part you need. Sadly I have no other specific source for IJ parts...but "RON" is an H&R specialists and,often, such persons often become involved with other brands of similar firearms he may have what you need or he may know who does.Check at:E-Mail to: mailto:email@example.com
and try our old friends at mailto:firstname.lastname@example.org