Na, naw, naw; I hear you thinking "but wait! If the outside of the case neck is fully supported in the die how can that be?!?"
Two reasons, in no particular order:
* - Your inner stem (the part that goes inside the case) flexes. After all the case neck is supported on the outside by the dagum hunk of steel that is the die. That makes the inner stem the weak link.
* - If the "outside" of the die that supports the case neck was a ".000000" fit you would either not be able to get the case in or out of it without one heck of a substantial amount of force.