Charles Ingram and Robert Webster were neighbors in Florida, but friends said the two older men had little love for each other and often quarreled. On a spring day in 2010, the two men, both gun enthusiasts who had state permits to carry concealed weapons, got into another argument across their lawns. This time, police later said, both men pulled out their weapons. When Mr. Webster began approaching, Mr. Ingram raised his gun, as did Webster. Two shots rang out simultaneously, and both men fell. Webster died almost instantly, Ingram less than a month later. That "Deadwood"-style neighborhood gunfight is...