I notice you are talking about setting up the dies for "new brass". You also mention that you have a couple of fired cases from his rifle. I'm willing to bet that if you take your callipers and measure them both you'll find that the fired brass is larger in all respects and are expanded to a replica of the gun's chamber dimentions.
Your full length sizing die will reduce fired brass to close to factory dimensions but it won't make it bigger so following RCBS's setup directions for the new brass will be perfectly safe. The directions that come with the dies are designed to allow for loading ammo for more that one rifle of the same caliber without changing the dies.
Once the brass has been fired in his rifle then you can reset the dies for "that particular gun" using using 17 Shooters instructions. If you do reset them for his rifle just make sure that you reset them if you load that caliber for a diffrent rifle or you may end up with a partially chambered cartridge stuck in the camber..
