Note: This requires the help of a friend. Play the "Stadium" level (Episode 3, Mission 11). Have your friend host the game. He or she will spawn in the elevator, and you will spawn on the field and can quickly collect the RPG. Enable the Aim Assist option so none of your shots miss. Get to the corner of the stadium, next to the RPG ammos. You should be able to target your friend's respawn point from this position, and can collect the nearby ammunition when needed. Have your friend repeatedly press [Use] to respawn immediately as you kill him or her repeatedly with one shot of the RPG.