I seem to have a problem when I type not everything gets put down for some reason, like something is updating.


Yes you're right, a rimmed case does headspace on the rim. I left the word like out. (with the shoulder pushed back it acts like a head space problem)

When I looked at your photo with the three loaded rounds and the case that had the neck split it is clear that the shoulders on the unfired rounds have the shoulder pushed back with a lot longer taper also they have a longer neck then the fired case does. Also you said that you "Brass p​rep consisted of running each case through the neck sizing bushing die and expander plug to iron out the necks" This I can see in your photo. Running a case through a bushing die can give you a eccentric case neck if your case is not fully in the shell holder or if the press ram is not in line with the die.
Also if that bushing die is made for a .45 parent case, like a .45-70 the larger diameter .44-77 case will not fit properly in the die body and it will leave a ring below the case shoulder.

My .44-90 bn cases below in my photo I had this problem also when I had the neck sizing die set to tight and it pushed the shoulder back and it stretched and pulled the necks off.

I'm glad you resolved your problem with the cases.

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