[DonVoigt]

It is an Erfurt Receiver, it has the Erfurt proof eagle, noticeably different from the Eagle applied at DWM by the govt. inspectors who visited or were assigned there.

The Crown over initial were applied by individual inspectors, and is thought to have been the first letter of their last name, those with an underline, were when two inspectors had the same initial.

The "RC" was an Erfurt applied marking(usually, but occasionally seen on DWM pistols); which indicated a part out of specification but deemed by the primary inspector(or group) to be acceptable. Since Erfurt was a royal arsenal, the RC were govt. employees; same as the inspectors who visited DWM to inspect arms.

One does not see the RC often on DWM arms, likely because any substandard parts were not applied as DWM had to guarantee all arms to be first class.

Above is not my info, but gleaned from books and threads here and else where.