melanie wrote:Body die just has the outside? No internal pin is that right?
Yes ,a body die only sizes from the shoulder ( head clearance) to the main body of the case . Does not size the neck at all .
So you neck size and decap primers in a separate die . That way when the case starts to get tight to chamber you size it in the body die but you are not upsetting the neck any . Also because there is no neck sizing going on at the same time you can size a very small and precise amount .
Allows for minimum resizing to get precise case fit and reduces work hardening of the brass . Also if a case does stick in the die it's very easy to punch out .
There is other uses also.