I usually use 1/3 of a pound of beef for a single patty and I used to pack them very tightly, so my pre-grilled burgers were at least the size of a normal coffee saucer and 1/4" thick; the post-grilled patties would fill an average bun. Even though I generally use 75/25 beef for burgers, they still end up a little dry for my taste. After some research and trial & error, I've finally figured out that my burgers were so dry because I was packing them too tightly.
Now I still use between 1/4 and 1/3 of a pound of beef per patty, but I very lightly pack the patties. The pre-grilled patties are now about 3/4 the diameter of their "tightly packed" cousins and are approximately 1/2" thick. I also add a nice dimple in the middle of each to hold my Lea & Perrins Worcestershire sauce while they grill. Now my burgers turn out much juicier and still fill an average size bun.
I've also applied the lightly packing tactic to my meatballs with equally satisfying results. So if your burgers, meatballs and other compressed ground beef dishes are a little on the dry side, try using less muscle the next time you prepare them.