Help--50 BMG sizing and neck tension
Its a long story but here goes:
I have two sources of brass, Lake City(once fired) and CBC (new Brazilian). Some cartridges made up from either source of brass allow the bullets to spin, only held in by the crimp. The CBC brass is thinner but it seems that all that matters is that the sizing die shrinks the throat inside diameter enough so that the expander button can size it correctly.
The die set is custom CH/4D.
The bullet diameter is .510 inches
The expander button in the die is .509 inches. The brass may (??) spring inward some after the expander button is dragged through it.
To me that does not seem like enough neck tension (0.001 inches). For brass this big what is a reasonable amount of neck tension?
I am thinking I need to make the expander button smaller but how much is enough to give a correct amount of neck tension?
That having been said here is what the ID of the throat is after sizing the brass without the expander button installed:
LC is .507 inches
CBC is about .510 inches
So the thinner CBC brass is part of the problem. The die body can not make it small enough for the expander button to do anything. Obviously the CBC brass is out of spec. At the cost of the 50 pieces of CBC brass, that is disheartening. Maybe I can make a Bushing and die body on my lathe to shrink the throat diameter of the CBC but this goes back to how much is enough neck tension for brass this big?
But is 0.001 inch neck tension really enoug for even the LC brass?