To compliment Gord's pictures, this is the full run on how I form brass.
The first is the '06,

second is an '06 necked up straight,

third is the necked up case then necked down to hold a .375 bullet by adjusting the FL die to properly place the shoulder in the correct location for a crush fit upon chambering.

fourth is a fireformed formed case,

fifth and sixth are .375/06Improved loaded rounds - 5/.- 270 TSX and 6/.- 300gr. Hornady RN300gr.