Even in the early 1800s some Americans painted an image of their countrymen as expert marksmen. A popular song attributed the American victory at the Battle of New Orleans in 1815 to the sharpshooting skills of the Kentucky militia. Yet Andrew Jackson, who commanded American forces in the battle, thought otherwise, and historians have agreed with him. Accurate guns were the exception in 1815 and for decades afterward. Balls exited smooth-bore muskets at unpredictable angles and started to tumble after fifty or sixty yards. In 1835 Jackson himself, now president, became a beneficiary of another feature of guns: their unreliability. A would-be assassin fired two single-shot pistols at Jackson at point-blank range. Both misfired.

It was not just the inaccuracy and unreliability of guns that made the sword and bayonet preferred weapons in battle. Guns were expensive. A gunsmith would count himself fortunate if he could turn out twenty a year; at the Battle of New Orleans, less than one-third of the Kentucky militia had any guns, let alone guns that worked.

Believing that the safety of the republic depended on a well-armed militia, Thomas Jefferson was keenly interested in finding ways to manufacture guns more rapidly. As president-elect in 1801 he witnessed a demonstration by Eli Whitney, the inventor of the cotton gin, of guns manufactured on the new principle of interchangeable parts. If each part of a gun could be machine-made and then fitted smoothly into the final product, there would be no need for the laborious methods of the skilled gunsmith. In Jefferson's presence, Whitney successfully fitted ten different gun locks, one after another, to one musket, using only a screwdriver.

Eager to stave off the impending bankruptcy of his cotton-gin business, Whitney had already accepted a federal contract to manufacture ten thousand muskets by 1800. His demonstration persuaded Jefferson that, although Whitney had yet to deliver any muskets, he could do the job. What Jefferson did not know was that Whitney cheated on the test: he already had hand-filed each lock so that it would fit. It would be another eight years before Whitney finally delivered the muskets.

Whitney's problem was that as late as 1820 no machines existed that could make gun parts with sufficient precision to be interchangeable. During the 1820s and 1830s, however, John Hall, a Maine gunsmith, began to construct such machines at the federal arsenal at Harpers Ferry, Virginia. Hall devised new machines for drilling cast-steel gun barrels, a variety of large and small drop hammers for pounding pieces of metal into shape, and new tools for cutting metal (called milling machines). With improvements by others during the 1840s and 1850s, these machine tools made it possible to achieve near uniformity, and hence interchangeability, in the parts of guns.

At first, Hall's innovations had little effect since the army was scaling back its demand for guns in the 1830s. The outbreak of war with Mexico in 1846 marked a turning point. Ten years earlier, a Connecticut inventor, Samuel Colt, had secured a patent for a repeating pistol with a rotating chambered-breech, usually called a revolver. At the start of the Mexican-American War, Colt won a federal contract to provide the army with one thousand revolvers. These proved to be of negligible value during the war, but Colt, a masterful publicist, was soon traveling the globe and telling all that his revolvers had won the war.

Eager to heighten the revolver's appeal to Americans, Colt made use of a recent invention, called a grammagraph, that engraved the same design repeatedly on steel. On the cylinders of his revolvers he impressed images of frontiersmen using their Colt pistols to heroically protect their wives and children from savage Indians.

In contrast to Hall, a man more interested in making than selling guns, Colt had a genius for popularizing gun ownership, not just on the frontier but also among respectable citizens in the East. He gave away scores of specially engraved revolvers to politicians and War Department officials, and he invited western heroes to dine at his Hartford, Connecticut, mansion. New England quickly became the center of a flourishing American gun industry. By 1860 nearly 85 percent of all American guns were manufactured there. By 1859 Colt had cut the price of a new revolver from fifty dollars to nineteen dollars.

As guns became less expensive, they became the weapon of choice for both the military and street toughs. At the Astor Place Riot in 1849 (discussed later), soldiers from New York's Seventh Regiment fired a volley that killed twenty-two people, the first time that militia fired on unarmed citizens. Murderers, who traditionally had gone about their business with knives and clubs, increasingly turned to guns. In the 1850s a surge in urban homicides usually caused by guns led to calls for gun control. In 1857 Baltimore became the first city to allow its police to use firearms. Confronted with an outbreak of gang warfare the same year, some New York police captains authorized their men to carry guns. No longer a luxury, guns could be purchased by ordinary citizens in new stores that sold only guns and accessories, forerunners of the modern gun supermarket.

Most states had laws barring blacks from owning guns. Women rarely purchased them. But for white American men, owning guns and knowing how to use them increasingly became a mark of manly self-reliance. Samuel Colt did all he could to encourage this attitude. When the home of a Hartford clergyman was burglarized in 1861, Colt promptly sent the clergyman "a copy of my latest work on 'Moral Reform,'" a Colt revolver. Two years earlier Dan Sickles, a New York congressman, had created a sensation by waylaying his wife's lover, Philip Barton Key (the son of the author of the "Star-Spangled Banner"), across the street from the White House. Armed with two pistols and shouting that Key was a "scoundrel" who had dishonored Sickles's marriage bed, Sickles shot the unarmed Key four times in front of several witnesses, killing him with the final shot. A notorious womanizer, Sickles had repeatedly cheated on his wife, but his behavior struck many men as justifiable. President James Buchanan, a political ally, paid one witness to disappear. Eventually, Sickles was acquitted of murder on the grounds of "temporary insanity." He continued to climb the ladder of politics and in 1863 he led a regiment at the Battle of Gettysburg.