This is a mysterious and very interesting issue. I sure can't see how a lead pellet could deform a barrel wall but I guess something did it and what else could it be?
As for Area 51. I took off out of Vegas once and was headed somewhere that was on the other side of Area 51. I was cruising along at about 10ft off the desert and at 5miles out of Vegas the tower comes on with "Ahhh, little red plane headed NW out of Vegas, do you realize where you're headed?"..... of course I answered, "Ahhh, no, where??"...
... all the while wondering how the hell they could see me from 5 miles away! I turned around and diverted before the F-16's arrived....