Prepare a gas or charcoal grill for high heat (425°F to 475°F), scrape the grate clean, and oil it lightly. Line a baking sheet with parchment paper and spoon some salt into a small bowl. Divide the ground beef into 6 mounds on the baking sheet. Scoop up a mound in each hand and judge their weight as best you can. If they seem about the same, put one of the mounds down and pick up another one, again judging its weight against the first. Continue in this fashion with each of the mounds, and add or subtract some of the ground beef to make them as equal as you can. (For complete accuracy, use a scale with a piece of plastic wrap over the plate.)
Use both hands to gently press one mound into a 1-inch thick disk about 4 inches wide. Then, rotate it between your palms to even up the edges without smashing it. Put the disk back on the parchment paper and use your thumb to make a quarter-sized impression about 1/4-inch deep in the center. Repeat with the 5 remaining mounds of ground beef and season both sides of the patties with the kosher salt. (If you will not be grilling the hamburgers within the next 15-20 minutes, cover and refrigerate.)
When the grill is so hot that you can only hold your hand 4 inches above it for 5 seconds or less, place the patties on the hottest part of the grill. Cook them for 3 to 3 1/2 minutes, then flip and cook for 3 to 3 1/2 minutes more for medium rare. (For medium, slide the burgers to the coolest part of the grill - or turn it off. Close the lid, and cook for 1 to 3 minutes longer.) Discard the parchment paper from the baking sheet and arrange the cooked hamburgers on it. If desired, grill your buns, cut side down for 1 to 2 minutes, and serve with ketchup and/or your favorite toppings.
Source: Curry, Lynne. "Perfect Grassfed Hamburgers." Pure Beef: An Essential Guide to Artisan Meat with Recipes for Every Cut. Pennsylvania: Running Press Book Publishers, 2012. 71. Print.