Stop in for a cup of coffee

So my daughter sends me a pic of what my SIL has found 5' down digging a grave (works in a graveyard). Holy heck it is a steel ball from grapeshot. Found at least ten of hem. WTFHarrisburg was targeted in the civil war but nothing happened. Any thoughts how theyg there? Have no idea if they trained in that area and if so do they ocassionally use grapehot? Pretty cool though. But 5' down?
Trench?