Just an alternate perspective to consider: For any cartridge that does not head space on the shoulder, so rimmed or belted cartridges, COW fire forming is a waste of powder, primers and Cream Of Wheat. In addition, AI cartridges were specifically designed so you can shoot regular loads in them and end up with fire formed AI brass so not a lot of benefit to COW forming those either.
If the cartridge you are working with do space off the shoulder and aren't an AI, just create a false shoulder on the neck. Fire forming loads will shoot almost as good as post formed so you might as well get the benefit of the extra shooting in if you are going to burn up valuable primers.