You are lying down.
You have a rifle.
You are firing lumps of lead and copper at (delete as applicable) Terrorists/Targets/Another Platoon playing The Enemy/The Russians/The Argentinians/The Chinese/Space Aliens/Zombies/Other(please state)........
The rifle jams half cocked due to unfired rounds sticking out of the breech.
In your panic, you try to push them back in with your fingertips.
The round obliges, going back into the breech and no-longer holds the cocking handle to the rear.
The cocking handle slides forward sharply, taking your finger with it.
There is blood.
You are now missing a fingertip, and have failed to kill your enemy of choice.