By Ben Marks — It used to be that if you felt the sudden urge to shoot something but found yourself without a gun, all you had to do was hop a streetcar to the local amusement park, stroll over to the midway, and toss a coin into the sweaty palm of a cigar-puffing carny. In return, he’d hand you a loaded .22 caliber rifle and wish you luck. Taking your place alongside other kindred shooters, you’d survey the cheerfully painted ducks, rabbits, cowboys, and Indians moving from side-to-side or bobbing before...