Hardness

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.

There are many hardness tests and scales. These tests are designed for different materials and their HT circumstance. For instance, the Rockwell "C" test uses a 45 degree diamond with 150 kg applied load. This is fine for through hardened material, but does not work for surface hardened material because at 150 kg, the diamond punctures through the hardened surface. In the instance of testing case hardened material, the Rockwell "N' test is quite popular, where the test difference is that the 150 kg load is replaced with a 15 kg load.ect. ect. Google is your friend!

The same hardness on a flat surface and round surface will measure differently. Not sure how many flat surfaces you will find on a bolt and receiver.

Along with what Steve said. This chart is fairly handy as well.

Hardness Conversion Chart - provides values for Brinell, Rockwell A, Rockwell B, Rockwell C, Rockwell D, Rockwell E, Rockwell F, Rockwell Superficial 15-N, Rockwell Superficial 30-N, Rockwell Superficial 45-N, Rockwell Superficial 30-T, Vickers 136,

AARONT said:

Along with what Steve said. This chart is fairly handy as well.

Hardness Conversion Chart - provides values for Brinell, Rockwell A, Rockwell B, Rockwell C, Rockwell D, Rockwell E, Rockwell F, Rockwell Superficial 15-N, Rockwell Superficial 30-N, Rockwell Superficial 45-N, Rockwell Superficial 30-T, Vickers 136,

Click to expand...

All very helpful, and all make perfect sense.

What would also be very helpful, but "my friend google" does not seem to agree, is a list of common material with what you could expect there Rockwell harness to be. Would real help people new to this get a overall view of where there results lie

Also, as my machine has only a C & B scale, I guess I can not test N15, just be removing some weights?

Thanks for all your help

Martin