I got very flat primers and brass flow at 65 grains, and lesser amounts at 60 grains. The 58-60 grain loads had similar markings to the winchester factory loads, but still more than I am used to with other chamberings. I don't know where the true max is supposed to be. I just know that I was getting pressure signs all the way down to 58 grains. Maybe they had the right charge weight and the wrong powder.