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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.
A lot depends are where you are testing. The entire bolt wouldn't be hardened, just the face.
There is a considerable difference in pressure generated by various cartridges of .308 bore diameter, and military rifles are built accordingly to handle the cartridges they were designed for; so you can expect variations in the heat treatments required. You say half finished bolt action rifle? Do you mean half finished action ? If so, has the action, bolt face, and lugs been squared ? This could affect your Rockwell readings based on the amount of material removed.
I would expect something over 15RC, even on a thin case hardened surface. Is the surface you are testing, flat and well supported? Any give at all will make a huge different in the reading.

Wouldn't any 'give' show up as a higher reading though? 17428
Good point. The 15RC just doesn't make much sense. Chin
This is an old post . I could give my own rather expert opinion but I am amused to read what has already been said. Plus by now the project has already gone on.. Notice that "expert" opinions should be circumspect. As a working tool an die maker with both heat treating furnace and a Rockwell hardness  testerI can tell you I have tested the hardness of every bolt and breechbolt I have ever dealt with.  That is all I will say other than a few degress of Rockwell C isn't gonna screw up your rifle. Have fun.