What effect does excessive copper fouling in the bore have on a bullet?

Excessive copper fouling in the bore can lead to a loss of stability in flight for the bullet. When copper deposits accumulate inside the barrel, they can alter the dimensions and finish of the bore. This buildup can affect how the bullet travels through the barrel, leading to increased friction and changes in the gas seal. Consequently, the bullet may not be stabilized properly as it exits the muzzle, which can result in erratic trajectories, reduced accuracy, and unpredictable behavior in flight.

In contrast, the other options do not accurately reflect the consequences of copper fouling. While it is true that excessive fouling can lead to increased pressures, that doesn’t directly reflect the stability of the bullet in flight. The idea that a bullet gains stability or becomes more accurate due to fouling is incorrect, as fouling disrupts the optimal environment for bullet travel and can cause various performance issues.