Fascinating to think that might be a .50 from 07 Dec 41. I don't know how well jacketed bullets hold up out in the weather, and I guess it would be impossible to tell, but...
Still fascinating, though. I sometimes wonder what kind of stories some of my older guns might tell if they could.
Ferinstance, I had an Amberg 1918 Mauser with the initials "EWL" roughly carved into the stock... and I've heard of a few examples of older milsurps having the issuee's name on a slip of paper under the buttplate or in cleaning kit compartments, etc.
If those old guns could talk.
Terry, 230RN
(Note: Some American .50s (APEI-169, M02 --grey/yellow tip) and some Japanese 12.7s were loaded with high explosives, so those might be considered unexploded ordnance.)