One of the secrets is finding the right ground meat, even at meat markets. The best kind is the whole cow ground up, midwestern, corn-fed beef, but you can't get it unless you special order it and pay through the nose, so I haven't gone that route yet and don't have a big enough freezer.
I usually buy ground chuck now at either one or two meat markets, ground round has good flavor but too dry, wonder how your recipe would work with half chuck and half ground round. Hmmmmm. Thank you for sharing that. If you cook hamburgers on charcoal, I'm not quite as fussy as to the kind of meat I buy, but it's too much trouble to start the charcoal just for me, and I need a new grill with a dome on it (for other things). They are almost $100 now. Even at Walmart.
This recipe works great even in a frying pan, it makes lean meat very juicy.