Damaged Bolt Knob

[kenhwind]

Awhile back I had noticed that there was a corner broken off of this bolt knob out of a Model 8 .35 Remington. So I found one on eBay and ended up with the winning bid. So the other day I decide to swap out the old bolt knob for the replacement I acquired. This is what I found:



This is the extent of what I remember the damage to have been.

Any speculation as to what might have caused this?

[h.charlie]

looks like inter-granular fracture, sense there doesn't appear to be any shearing I would say its just a old part that had some structural flaw in the metal when it was made and over time just work its way out, although at the front of the operating handle mine are all flat your seems to have a bit more then mine or it could just be me staring at the picture for to long.