Forming from 6.5G with Mighty Armory die

[Old Bob]

If you resize the Grendel brass in a Hornady 6 ARC die without the de-capping rod/neck expander installed, the case necks will be undersized for the trimmer pilots used in piloted case trimmers like RCBS or Lyman. Little Crow or L.E. Wilson trimmers are what you'd need for trimming. Or, you could reinstall the de-capping rod/expander & run your brass over it to expand the case necks while being careful not to crush the shoulders. Just don't run the cases back up into the neck area of the die. Another way would be to use a neck expander die with a .241" mandrel. That's what I'm doing now. You can get mandrels in other diameters. It depends on how much case-neck/bullet tension you desire.