this brings up an interesting ? to those that toss/form their own burgers. I find i get a better burger if cooking a day later-i.e. well defined r/m/w ranges.
only thing i can come up with is letting the protiens relax and...
you're whipping by hand? that may be one of the probs. don't get me wrong, meringues have been beaten by hand for quite a while, but do yourself-and your arm-a favor.