Did the Framers of the Second Amendment consider the possibility that Americans might own firearms with a capacity greater than 10 rounds? Certainly yes. Such arms had been invented two centuries before the Second Amendment, and by 1791, repeating arms, including those capable of firing more than 10 rounds, were well-known in the United States. The history is explained in a Third Circuit amicus brief I coauthored last week.
Some of the material in the brief is covered in more detail in my article The History of Firearms Magazines and of Magazine Prohibition, 78 Albany Law Review 849 (2015).
Earliest repeating arms: A repeater is a firearm that can fire more than one shot without having to be reloaded. The first known repeating firearms date back to between 1490 and 1530, with guns that fired 10 consecutive rounds. A 1580 gun could fire 16 shots. Once the user pressed the trigger, these guns would continue to fire until the ammunition was exhausted.
Seventeenth century: By the 1640s, major improvements in repeating arms had been developed. Now, the user could fire just one shot by pressing the trigger, and then fire more shots by pressing the trigger repeatedly. Danish rifles invented by Peter Kalthoff had ammunition capacities ranging from 6 to 30 rounds. During the seventeenth century, Kalthoff repeaters were copied by gunsmiths from London to Moscow.
At about the same time, the Lorenzoni revolver was invented in Italy, with a typical capacity of 7 shots. Like semiautomatic firearms (invented 1885), the Lorenzoni could self-reload. To fire the next shot, the user did not have to move a lever, bolt, or pump; the Lorenzoni could fire as fast the user could press the trigger–similar to modern revolvers or semiautomatics. The Lorenzoni was manufactured far and wide–including in New England. Famed diarist Samuel Pepys was much impressed with a demonstration he saw in London in 1664.
During the Revolution, inventor Joseph Belton demonstrated a 16 shot long gun. Witnesses, including Gen. Horatio Gates and scientist David Rittenhouse, were impressed, and the Continental Congress negotiated with Belton for a large order, but Belton wanted more money than Congress could afford.
Also during the Revolution, the British introduced their six-shot Ferguson Rifle (which might have made a difference in the war, if the British had manufactured enough of them) and the Nock Valley Gun (which shot seven rounds at once).
Early Republic: By the time the Second Amendment was ratified, the state-of-the-art
repeater was the Girandoni air rifle, which could shoot 21 or 22 rounds in .46 or .49 caliber. Although powered by compressed air, the Girandoni was ballistically equal
to a powder gun, and powerful enough to take an elk with a single shot. Many air guns of the time were equally powerful.
Originally invented for Austrian army sharpshooters, the Girandoni was manufactured in Russia, Germany, Switzerland, England–and Pennsylvania. Meriwether Lewis bought a Pennsylvania model, and carried on the Lewis and Clark Expedition. The gun is mentioned 22 times in Clark's journal–usually in the context of the expedition showing off the gun to Indians, making the implicit point that the expedition could defend itself against a larger group.
Early America: The Kalthoffs and Lorenzonis were not the only repeaters made during the century. For example, in the mid-1600s, some American repeaters were manufactured with revolving cylinders to hold the ammunition. Unlike the revolvers perfected by Samuel Colt in the 1830s, these revolvers required the user to rotate the cylinder by hand after each shot.
The French in North America had their own repeaters. For example, in 1690 the Comte de Frontenac "astonished the Iroquois with his three and five shot repeaters." 1 Charles Winthrop Sawyer, Firearms in American History 29 (1910).