You really need to test the lug on the flat side.
Testing on the curve surface causes some error.

For reference a good knife blade is about RC 55 and a REX 95 tool bit is about RC 64.
I believe I tested a Remington 700 bolt at 42 or so.

the area outlined in red is often referred to as "crystallized".....in fact this is typical of metal fatigue and is an excellent sample of this.

While I agree that the hardness testing should not be done on the radius, the hardness numbers are so high that I'm convinced the readings are close to correct.

Further, the rockwell tester is applying (from the photos) 150 KG load whick means the hardness is quite deep.

It seems from the evidence so far that we have a classic case of metal fatigue.....did we say the barrel had been replaced?.....

I stand corrected, thanks for being patient, ireload



62 hardness?

WOW

jeffe

quote:

Originally posted by jeffeosso:
I stand corrected, thanks for being patient, ireload



62 hardness?

WOW

jeffe

Yes Jeffe, and notice that there is no case boundry around the failed surface which suggests this is not case hardened but thru hardened...

Some hi carbon steel!!!

I understand some folks today are making bolts from 8620 steel and case hardening it.....which makes a lot of sence after seeing this photo....bear in mind that this thing saw a lot of firings....but still should not have failed.