Final answer:
The main difference between a shotgun and a rifle is the barrel. Shotguns have smooth bore barrels that aren't rifled, which causes fired pellets to spread, making them suitable for short-range targets. Rifles have rifled barrels that spin bullets for stability and accuracy at longer distances.
Step-by-step explanation:
The primary difference between a shotgun and a rifle lies in the construction of their barrels. A shotgun typically has a smooth bore barrel, meaning it is smooth on the inside and doesn't have any rifling—the grooves and lands that spiral down the inside of a rifle's barrel. This rifling is what imparts a spin to the bullet, giving it greater stability and accuracy over longer distances, which is characteristic of a rifle.
In contrast, shotguns are designed to fire shells that contain numerous small pellets called shot, or sometimes a single slug. Without rifling, these pellets spread out after leaving the barrel, making it easier to hit a moving target at shorter ranges but with less precision at long distances. The smooth bore barrel of the shotgun is what primarily sets it apart from the rifled barrel of a rifle.