I scratched the bolt with a 3" 16d steel finish nail and it was pretty tough. Didn't make much of a mark on the bolt at all. After some pressure and scratching several times it really didn't mark it much more, very light scratches, and really only seemed to get past the oxidation layer exposing brighter brass.

I'm guessing this tells us the lock is an older vintage rather than a younger one?

Your help is appreciated,

B.