Make your patties as thin as possible without them falling apart, I use a piece of foil, lay my patty on it and flatten it with my fingers or a rolling pin or the bottom of a pan.
Use a med-high flame on your grill, let the grill get good and hot with the lid closed. Put your patties on, close the lid, after about 7ish minutes, flip your patty, cook another 7ish minutes. The fat from the chuck drips onto the fire making it flame up and cook. That's where all the flavor comes from. I never even season my patties anymore, just put them on plain. My family as well as myself are asthonished everytime I make these, taste just like BK.