How can I keep my burgers flat? I have tried to keep my burgers flat for a while but they always end up turning into a ball and I have to flatten them out as they cook, even tried the little hole in the middle of the patty but it doesn't work.

It's ground beef (90/10 angus beef) and I'm only adding salt and pepper before i shape them. I am doing 8 oz patties and grill at medium high temp.

Ok the inflation is gone, put no salt on it and added a bigger dimple. Now my second question would be, what can I do to keep the meat together?. Sometimes about 30% of the times it breaks a little from the sides.
Many chefs in the USA recommend pressing a large dimple in one side of the meat patty before cooking it on the nondimpled side first, to prevent the problem you are experiencing