On Thu, 12 Nov 2015 00:04:15 -0600, wrote:

A friend has the bullet that was removed from his dad in WW II. 8mm
German; it has a blue core. What would that core be?

This bullet is one of five that hit him. This one passed through his
pelvis and was removed from under his armpit.

Here is photo.
https://www.shutterfly.com/lightbox/...fd7207a7b1fe91