1.) Put an M203, GL1, etc on the under barrel of an assault rifle and have NO GRENADES
2.) Switch to HE Round mode on your Assault Rifle
3.) Fire a waste shot and QUICKLY switch to Secondary without letting the gun reload
4.) Switch back to Primary and QUICKLY switch to AUTOMATIC and double tap X
5.) Switch to SINGLE shot and fire off a single round

YOUR DONE! IT WORKS MOST OF THE TIME BUT NOT ALWAYS! BUT HAVE FUN!