Instructions
Begin whichever "Resident Evil 4" saved game file that has the rifle. Press the "-" button on the Wii remote once the game loads. The main inventory screen will appear. Move the Wii remote to hover over the rifle and press "A" to equip it. Press the "-" button again to resume normal gameplay.
Press the "B" trigger button on the back of the Wii remote. Leon will bring the rifle to his shoulder, and the rifle's crosshairs will appear.
Move the Wii remote to move the crosshairs. Press "A" to fire the rifle. If you move the crosshairs to an enemy's' head, you will typically kill the enemy in one or two shots. If you move the crosshairs to an enemy's legs, you can drop the enemy to his knees and slow down their progress.