Re: Chambering problems?
If teh case neck split on new brass then it might be that the necks were not properly annealed at the factory.
If you have a concentricity gauge check the fired brass. If you don't have one then roll a couple of cases around on a table and see if they jump and bump around which will mean a bad chamber.
Most likely problem is in the FL die. If you have some brass you have not run through it yet, try chambering that brass in the rifle. If the new unsized brass chambers fine then its the die.
The Smokin Fur Rifle Club