In the opening scene, when the camera turns the corner, you are able to see the characters were waiting for the signal to start walking.
When the sniper is setting his rifle up he reaches for a bullet located above his ear. The bullet primer has a detent indicating it has been previous fired. Even if the bullet was reloaded the primer would have needed to be replaced in order for it to be fired again.
Near the end when Boone and Marquette shake hands, the Skrill is missing.