I could be wrong on this one, but I was of the opinion that many Mausers were "Selectivly" case-hardened Ie only in areas where needed as on the bolt lug seats etc. Many will give a soft reading if checked on the receiver ring etc, but are properly hardened where essential. It may well be noted that German custom makers follow several practises that are frowned upon by "Conservative Americans". A couple in addition to the CC that comes to mind is converting J bore 8MM to S bore by increasing the bullet seat dia & adding a longer leade as well as cutting those humongus dovetails for a claw mount block across the top of the receiver ring. Everyone just has to choose what they are willing to risk.
Personally I am of the opinion that a C-scale penertrator would break through the normal depth of case on a CC-hardened surface & the reading would be of little use.
