The differences in performance were striking. In a competition between Minié rifles and smoothbore muskets, 20 men fired 10 shots with each weapon, or 200 rounds per gun, at a target 6-feet high and 20-feet across meant to represent an enemy unit. At 100 yards, 149 musket shots hit (74.5 percent) compared with 189 Minié shots (94.5 percent). But at 400 yards, just nine (4.5 percent) musket shots found their mark; the Minié rifle hit 105 times (52.5 percent).

So it was that Mordecai and his fellow Ordnance men believed they were developing a rifle that was more innovative than any untried breechloader or repeater, and that far surpassed the “ordinary muskets” being issued to European soldiers. To Davis’ surprise, then, Mordecai did not report on what Americans could learn from the Europeans, but actually confirmed that they were already ahead of them!

The rifle in question was the .58-cal. U.S. Model 1855 rifle-musket, a design that marked the end of army production of smoothbores. Along with its Minié mechanism, it came equipped with a state-of-the-art Maynard priming system that used a roll of percussion caps to ignite the powder.

When the commissioners departed for Europe in April 1855, the new rifle was still awaiting approval from Davis (given on July 5), but in 1857 it went into production at Springfield and, two years later, at Harpers Ferry. Though the South enjoyed a windfall of Model 1855 machinery after the capture of Harpers Ferry, in the North the model was manufactured until only mid-1861, when it was replaced by Ordnance’s newest upgrade, the Model 1861. Roughly 750,000 were made, to which must be added more than half a million Models 1863 and 1864 (which were enhanced versions).

Given that only around 60,000 Model 1855s were produced, the arm may not have enjoyed the success of its replacements—partly because it was not quite as excellent a piece as advertised—but as Mordecai’s pride and joy it served as the patriarch of a family of army rifles whose influence would last at least until the advent of the M16 in the 1960s.

The critical importance of the Model 1855 dynasty lay in Mordecai’s fascination with range and accuracy—attributes that he could precisely measure, quantify, standardize, classify and compare. What mattered in a rifle, he believed, was its ability to allow a soldier to shoot his target at the longest distance possible and with the bare minimum of ammunition. To Mordecai, marksmanship was all, and in this he was adapting the historical American talent for fine shooting to the scientifically minded Victorian era.

Marksmanship was key because Mordecai was confident that in future wars combatants would need to be at least 400 yards apart owing to the introduction of the devastating Minié bullet. Human conflict was to be a long-range affair, for which neither breechloaders (that lacked range owing to gas-leakage) and repeaters (that lacked accuracy owing to their rapid firing) were suitable.

In this estimation he was disastrously wrong. In fact, as a sustained analysis of the Civil War’s battles, skirmishes and actions reveals, the average distance between the two sides during a firefight was a mere 127 yards.

Amid the mud, roar and terror of the front, Mordecai’s dense computations and rational assumptions were rendered meaningless. The future was seemingly mortgaged to firepower, exemplified by soldiers’ close-range use of buck n’ ball (a .69-cal. ball and three buckshot) and the post-war rise of the breechloading repeater.

Nevertheless, Mordecai got one big thing absolutely right: No matter with which arm, sound shooting—honed by practice, personal self-discipline, mastery over one’s firearm and coolness under pressure—was what distinguished soldiers from savages, Americans from suborned troops, professional warriors from raw conscripts.

Mordecai himself stood aside from these developments. After the first guns were fired, as he put it, “in that Calamitous Conflict,” Mordecai resigned his commission “for reasons peculiar to myself.” His “peculiar” reasons were that as a moderate, Southern-born Democrat and an individual of self-confessedly robust “conservative opinions,” Mordecai grieved for the North’s abolitionist “interference” in affairs below the Mason-Dixon Line, but he had “no sympathy” with slavery and he was a good and faithful servant of the federal government.

Mordecai’s loyalties were thus cruelly divided, and his only means of reconciling them was to avoid the company of “fanatics, North or South.” Though as the country’s leading ballistician Mordecai was offered high-ranking commissions by both the Confederacy and the Union, he refused them so that he would never be forced to choose a side. So it was that on May 2, 1861, the 57-year-old Mordecai deliberately sacrificed his hopes of higher rank by departing his beloved Ordnance Dept. (though not before recommending to Davis that his deputy Josiah Gorgas serve as Ordnance chief). He and his family moved to Philadelphia to wait out the war. After Appomattox, Mordecai joined the Vera Cruz and Mexican Railway as a senior engineer, but later returned to Philadelphia as secretary and treasurer of the Pennsylvania Railroad, dying at the age of 85 in 1887.

By that time, he at least had enjoyed the satisfaction of seeing the United States Army, hoping to avoid another bloodbath like the Civil War, adopt the strictest principles and practices of marksmanship, a policy that turned its men into the most lethal soldiers, shot for shot, in the world.

And so his ghost lived on. By preserving marksmanship as the quintessential American trait—a belief adopted by the nascent NRA from the 1870s onward—he can be counted as the spiritual father of such fine-shooting legends as the Springfield Model 1903 and the M1 Garand. It was a proud legacy for this unfairly obscure weaponry wizard.

Alexander Rose is the author of “American Rifle: A Biography” and “Washington’s Spies: A History of America’s First Spy Ring.” His Web site is Alexrose.com.