I have been trying various powders and seating depths with 168 grain nosler ballistic tips. I've tried IMR 4350, H4381 RL 19,22, H 4350, H4381 sc and H380. I loaded these powders and COAL was to max mag length at 2.858. I started out 4 grains lower than max load for each powder and worked up. Every powder shot better as I approached max load. The powder that shot the best was H4350. My problem is that it shoots the best 1 grain over max listed load at 66.5 grains. I've tried from 60.5 grains and worked up thinking I might hit another node at a lower charge. No luck. At 65.5 grains I get an average group of 1.1 inch. At 66.5 grains I get 0.55 inch. Over the chrony I got a 5 shot average of 3198 with ES of 11. I am getting weird signs of pressure. For the most part the bolt does not stick, No marks on back of case, primers look good. I shot 45 rounds at 66.5 grains. The first 3 rounds the bolt was slightly sticky but the rest were fine?? I had 1 case have a hole blow out around the primer. Cases are winchester, trimmed to 2.090. Primers are win mag primers. As I drop 0.10 grain in powder the accuracy drops off. I have attached a pic of the blown primer pocket. Over pressure or bad case? Why would only 3 shots produce a sticky bolt. Rifle was just cleaned prior to shooting. I have also tried loading 5 to 20 thou back from lands. Pretty much same results. I just picked up some 180 grain accubonds and 155 grain bergers to try something Anyone with any pointers? I'm at a loss?