Lee seating dies have a built in crimp (at least all the ones I use) You need to use a nickel or other spacer to keep the seating die from coming into contact with the shell holder. Put the ram at the highest position, screw the seating die down until the base of the shell holder is in contact with the nickel. Then verify that there is no crimp by seating a bullet.
If you are using a FCD after seating that is a different process.
Machine guns are awesome until you have to carry one.