2 thoughts; with the factory cases splitting ?? how many are split, where are the splits, are they of only one headstamp?
What make of rifle/barrel? is this a custom or other make that could have a out of spec chamber?
#2 the reloaded round should not be a tight fit in the chamber. Normally adjustment of the resixing die in the press until the resized case enters the chamber freely is a good fit of the case to that chamber.