“Do you have the kind of bullet that killed Lincoln?” asked a tourist buying a Derringer pistol, wearing a God Bless America t-shirt. I looked up from the counter a bit confused. I’d come in late after watching Steven Spielberg and Doris Kearns Goodwin speak at Gettysburg’s Soldiers’ National Cemetery for the 149th Remembrance Day, the anniversary of Abraham Lincoln’s address. I was cold and my coffee had only begun to wake me up.

“It should be the size of …