Hardness

[Longsilver]

Hoping someone out there can shed a little light on this!
 
I recently acquired a very nice, half finished bolt action rifle in 308. A thought it would be a good idea, before I went to the effort of finishing it, that I test the hardness of the action and bolt. That part apparently having been finished hardened and blued.
 
Having always wanted a Rockwell harness tester, I managed to find a second hand one in good condition, and at a reasonable price.
 
After and watching a few youtube clips, I thought I had got the measure of it, especially after I checked the test pieces, that came within 1 point of the expected 61RC.
 
I then tested the action, and bolt face, and was very surprised to find they came in around 15RC !  This was a complete shock as my best scriber just slides off, not leaving any mark!
 
So I then went on binge test anything to hand
 
Mild Steel 14RC
HSS tool steel 63RC
Gauge Plate (untreated) 14RC
 
Then Gun parts
 
P14 Bolt 52RC
Winchester 70 Bolt 42RC
P14 action 39RC
Enfield Mk4 bolt lugs 37 to 63RC dependant where you measure
 
And strangest of all, I tested 3 Enfield Mk4 actions and they all came in at around 15 RC
 
Can anyone help to explain the low readings on my new action and the Enfield Mk4. Is my machine inaccurate at the low end, or does case hardening have something to do with it.
 
Any help gracefully received.
 
 
 Martin