On original rifles, case hardening was an "extra" not included on standard guns. It tends to fade when exposed to sunlight so few original case hardened rifles show much finish now. Blued receivers wear better.
I did some number crunching from the Herbert G. Houze "The Winchester Model 1876 Centennial Rifle" book and came up with 4,141 Model 1876 rifles and carbines that had case hardening. Since 63,871 Model 1876 rifles, carbines and muskets were made, that means about 6% of them had case hardening.
Here is a case hardened receiver on an 1884 vintage Model 1876 special order rifle. Note the finish.