Case Hardened Levers on Sav 99's??

Hi, was wondering if there was any info on the web about which specific models of 99's had the case hardened (instead of blued) coloring on their levers? Was there a certain year or certain 99 models that Savage began that process? I have a couple of older 1920's+/- 99's that the metal is a completely worn to steel coloring nearly all over and don't know if the levers were ever case hardened from the factory or not. I could not find this specific info on the Savage99.com web site. Thanks in advance for info along these lines.

Yes they were all case colored, not sure when or if they were ever blued but I'd hazard a guess at the 1,000,000 serial range.

Brain fart right now and I don't have my books with me.

Joe, if I remember correctly there were some blued levers between 1974 and 1977.