This Colt M1911A1 was shipped on March 29th, 1941 to the Commanding Officer at Springfield Armory in a 2,000 gun shipment.
This particular pistol has a number matching slide, RS final inspectors mark but an CSR inspectors mark for the lower assembly.
During the assembly of these pistols the inspectors would perform a function check on the lower assembly. If a pistol lower were to pass it would get an inspectors stamp on the top of the frame next to the disconnector hole. Once the upper assembly was added and the entire pistol passed it's function check the inspectors stamp on the frame below the slide stop was added.
Timing of the change of oversight on inspectors allowed for the the dual inspectors on this particular pistol to take place. There have been other pistols in this serial number observed at the time of this writing.
The inspector stamp of C.S.R. is for Charles S. Reed. From August 2nd, 1938 to December 31st, 1940 he was in charge of the production and acceptance of ordnance in the Springfield Ordnance District. He was the officer in charge of the Outside Inspection (A.I.O.).
The RS Inspection mark is for Colonel Robert Sears. Col. Sears was the the Army Inspector of Ordnance at the Hartford Ordnance District office from August 3rd 1937 - June 30th, 1941. His inspection mark is seen on pistols in the 723000-750500 range.