Jim
With out seeing the cases , i'd would have to say these signs are from the cases not fitting the chamber properly . what i mean is that the chamber is larger than the die sized case . was this the first firing of these formed cases ?
If this is the case try just neck sizing the brass now that they have been fire formed to the chamber , that should cure the problem of the cases sliding back and putting marks on the head , as for the black neck it could be a case of the neck not expanding to fill the chamber due to a low pressure .
Just a couple of ideas to throw at you . i have a 30/30 that no mater what i do i still get some black on the neck even at MAX load , i will have to do a chamber cast to see if the neck is just to large but it still shoots very well . may just have to live with the black .
stimpy