Riding Shotgun

Guards genuinely did ride alongside stagecoach drivers in the American West, armed and ready to fend off bandits, especially when a coach carried valuables like silver bullion. Shotguns suited the job well, since their spread made it easier to hit a fast-moving target at close range. The trouble is the actual phrase "riding shotgun" doesn't show up in any 19th-century account of this practice at all; the earliest known use is in a 1905 novel, and the phrase only became genuinely popular decades later, through Western films of the 1930s and 40s like Stagecoach. The practice was real; the specific wording came along much later than the era it describes.