When confronting Tuffurd, Cogburn slams a pistol cartridge against a piece of furniture, and it fires. Slamming a bullet against a smooth surface would not work, unless there were a protruding nail or other sharp point to depress the pistol primer.
At 1:20:27, the primer of the pistol cartridge is already depressed, with a small dent in the middle. This means it is spent, and will not fire. An unfired primer would be smooth.