From John Hennessy:

The discovery last week of bullets imbedded in a tree at Gettysburg reminded me of a transient mystery from my Manassas days.  Out in the area of Groveton woods–a couple hundreds yards east of where Porter staged for his August 30 attack–there stood a decrepit barn that once had been part of the farm of Montgomery Peters, a postwar resident on the battlefield. Like its owner, the barn was postwar too–we knew that–and so there was little urgency to halt its deterioration (the attitude would not be as dismissive today), which by the time I encountered it was decades old. Finally, the place just had to come down, and the park’s maintenance staff went at it.

Some of the timbers were ancient and huge, and when they cut into at least one of them, they found it contained several Civil War bullets.  But…the barn wasn’t there during the war?  A scramble to the source material confirmed that that was undeniably true. After some puzzling, we soon realized that the timbers had probably been cut from the adjacent woods, which had been the scene of heavy combat….

And that’s how bullets from the battle ended up in a barn that wasn’t there….