I loaded some rounds a few days before hunting season with my 300WSM, and things went fine. I had no time to spend in load development, so I used the 3 loads recomended in the manual with IMR 4064 shooting 150gr bst nosler bullets. They were 56.5 58.5 and 60.5 grains. None showed signs of pressure at that time and I went with 58.5 for hunting. I now have time to experiment more with these loads and loaded 6 loads starting at 56.7 up to the max moving up in smaller incriments. I had just cleaned my rifle so I shot a fouling group of 3 with the 58.5 grain loads I hunted with. Then on to the optimum charge weight procedure as has been described here. first shot 56.7 shot fine second 57.6 shot fine third 58.9 Bolt hard to open and ejector mark on face of case I inspected the rifle, took a walk to the target and returned a few min later. Things looked fine and a I fired another 56.7 which was fine. I fired a 57.6 and that also was hard to open. I stopped there and went in. I'm using once fired brass, full length sized winchester WRL primers. All of the rounds chambered easily. I'm wondering why I had no problems the first time around up to 60.5 grains, and now having problems with lighter loads. All of the components and procedures were the same, the only change really was cleaning the rifle and Tepmerature which was less than 10 degrees warmer the first time. Any ideas?