mrcvs said

Flaking receivers typical of rifles and carbines from the teens or 1920’s, is the flaking a consequence of time & aging or is it due to wear/use and even possibly abuse?  

Flaking was the result of increasing the nickel content of the alloy used for rcvrs. in 1919.  This could have been alleviated by rust bluing, as on brls, but rcvrs. were “machine blued,” a variant of the carbonia process.  In 1939, company changed to the DuLite bluing process, which solved the problem.