How can I stop my burgers from shrinking so much?

Your cooking methods are all correct, it's your ground beef that's shrinking. The least expensive "ground chuck, or labeling of 77/27, 70/30, 80/20, 90/10 are a sure tale sign of the meat ratio to fat ratio, in that order. 90/10's won't shrink much, seeing as they have little fat, but are best cooked medium rare to medium (at the most) and tend to taste quite dry and tastless after those temperatures unless you have some killer dressings and accoutriments. 77/27, or 70/30 have greater fat content and naturally, add more flavor, but the shrinkage value is huge. For my burgers, I find that the 80/20 blend is perfect, yes, you're going to get some shrinkage, but the fat content is enough to give the burgers some flavor withhout major loss in size upon cooking them. So, hope some of this information helps you to pick out the best hamburger meat with the cooking application you are making this day. If you have further questions, please don't hesitate to email me and have a great Monday night!