How can you get the infinite rocket launcher in resident evil 5

Stick your thumb up your butt, close your eyes, yell out "I'm a pretty (gender here)" then click your heels together three times, and a magical fairy gives it to you. XD
haha that's a funny bast*** above me, anyway you can only get it if you beat the game in under 5 hours best to do it on amateur level! but once you get it its pretty much no sweat completing the game on all the difficulty levels. When you have completed the game in under 5 hours you just enable the unlimited ammo aption, in bonus features.