Which of the following is NOT one of the NRA's fundamental rules of firearm safety?

The principle that is NOT one of the NRA's fundamental rules of firearm safety is related to the practice of handling firearms while under the influence of alcohol or drugs. Firearms should always be used responsibly, and targeting practice or handling firearms while intoxicated can lead to dangerous situations and accidents. Practicing firearm safety emphasizes a clear mindset to ensure both the safety of the individual handling the weapon and those around them.

The other options listed are foundational guidelines that are crucial for safe firearm handling. Always keeping the firearm pointed in a safe direction prevents unintentional discharges from causing injury. Keeping your finger off the trigger until one is ready to shoot is a key practice to avoid accidental discharges. Finally, always assuming a firearm is unloaded until it has been proven otherwise is essential in establishing a safety-first approach to firearm handling, ensuring that individuals verify the weapon's condition before engaging with it.