Why?
After Winchester purchased Cooey in 1961, they continued the 84 for a few years before rebranding it as the Model 840 in 1967 to reflect production changes and economization. Cooey Model 840 Serial Number Lookup
While there is no centralized database for Cooey Model 840 serial numbers, there are several methods you can use to lookup your rifle's serial number: Cooey Model 840 Serial Number Lookup