What you've got is a bullet that was so tightly jammed in the barrel that the soldier darn-near completely "cored" the bullet in his attempts to worm it out. I've found a couple of very similar ones over the years here relic-hunting here in Virginia.
The soldier was using both a "double helix" bulletworm and a "screw" bulletworm. The screw-type worm dug down all the way through the bullet's nose until it even pierced into the cone-cavity. At that point it had no "traction". So the soldier switched to a double-helix worm, which ate away the rest of the bullet's interior - but left a thin outer skin of lead as it burrowed deep down into the bullet. The result of all this labor with the two worms looks kinda like a thick-based tin can - but made of lead.
When the soldier finally got that ultra-stubborn bullet out, he was so frustrated with it he bit it.
Like I said, I have a couple like it that weren't bitten. On them, you can clearly see the evidence of the two different types of bullet-worms ...which I have tried to "visually describe" for you in the paragraph above. I hope my "verbal picture" of what happened is sufficient for you to visualize it.
Regards,
TheCannonballGuy [Pete George]
