I need some help please. I have not been reloading that long, but I have reloaded for several different calibers and have a good grasp on things I think. This has never happened before! The rifle in question is my Mark V .30-378. It is unmodified, except for a trigger job and a B&C stock. It gets cleaned regularly. It came with about 40 brass, some of which were never fired factory rounds, and some that had been loaded once or twice. The rifle has not had much use, and should have a pretty low round count.. The brass: I have never annealed them. I do not have a tumbler, I just use compressed air to clean the insides. Yes, I lube the cases, and brush the insides of the neck. They have never been neck turned as I do not have one. I just use basic full length RCBS dies. These were loaded with 117.5 Gr. of US869 behind a 200 Gr. Barnes LRX. CCI 250 primers. Length is slightly longer than factory spec, but they are still 0.4" off the lands. Factory 26" barrel, and velocities are around 3165 These have only been fired 2 or 3 times (different load with 175 gr. barnes.) At the moment every single case with this new load is coming out of the chamber with a crack at the shoulder/neck. I have already ruined about 15 brass because the bolt opens easy still and I didn't notice it right away.. I would like your opinions on what you guys think is causing this. I am a little confused, because there are no other pressure signs, the bolt opens just fine, it is not even the least bit sticky. These spent brass go into the chamber fine still, and are not tight. The primers look ok (to me.) All measurements I have taken on the cases (loaded and fired) seem to be within spec. I am currently in the process of pulling all my bullets apart, and I plan to anneal them all and start over, possibly with a different powder. I know these loads are hot, but according to Hodgdons I am 1/2 Gr. off max still. Are these just too hot? Or, is there maybe some other factors at work here? I crushed the necks on some of these with pliers and they were really brittle. Thanks in advance.