Need help regarding my FieldMaster 121 rifle

[John Gyde]

The EUU is not the serial number, but means the rifle was sent for repair in Oct 1949. There should be another date code that will give you the month/year of production. There also should be a serial # on the side of the receiver.

[John Gyde]

That's the serial #. It would indicate production in 1949. The "3" indicates that it was returned to the factory for repair. Maybe it's part of the testing and proof stamps.