Final answer:
When a cartridge fails to fire after the primer has been struck, the shooter should keep the gun pointed in a safe direction.
Step-by-step explanation:
When a cartridge fails to fire after the primer has been struck by the firing pin, it is called a hang fire. In such a situation, it is important for the shooter to keep the gun pointed in a safe direction. A hang fire is a delayed ignition that can still occur even after the primer has been struck, so the shooter must exercise caution and be prepared for the cartridge to fire unexpectedly.