Re: What would cause a case to split!!!!??
If the brass is new then the best thing to do is reduce the load down 10% for the first shot and jam the bullet into the lands but don't extract before firing . This way the case head will not expand backwards . That should blow the shoulder forward taking up any excessive head clearance .
That should fix the problem for that batch of cases while you only have to neck size but as soon as you need to body size it may cause the same issue again if the chamber is cut too deep and a standard die will not reduce the base to fit before it bumps the shoulder .
You keep sizing to fit the case back in but by the time it does fit the shoulder has been bumped too much .
I would definately take it back to the gunsmith and ask for the head clearance to be checked again and make sure you take the head seperated case with you and a few of the other new unfired cases and mention that you think the gun is dangerous .
That should motivate them to check it out properly .
If the chamber is in spec then the suspicion falls on the new brass or the sizing system .