By the time American settlers began moving westward, which firearm was the most commonly used?

The firearm that was most commonly used by American settlers moving westward was the flintlock. During the period of westward expansion, flintlock firearms were widely available and commonly used due to their relatively simple design and reliability. These firearms utilized a flint mechanism to ignite the gunpowder, allowing for effective shooting.

As settlers faced diverse challenges in the frontier, the flintlock rifle, in particular, became popular for hunting and protection. It offered greater accuracy compared to other firearms of the time, making it suitable for both larger game during hunting and self-defense scenarios.

The other options, while significant in different contexts, did not see the same level of use among settlers during this specific historical period. The revolver, for example, became more prominent later in the 19th century; shotguns were primarily used for bird hunting and were less versatile for the types of game encountered in the West.