I have had some great advice from guys on here regarding the case prep for the new Nesika I have.
I need some help fireforming. I have some new 243 Lapua brass that has been turned to give .268 when loaded, so that bit should be okay..

To fireform, what is the best method?
Faster powder with bullets into the lands or just my normal 243 load (Varget 41.5 grains and 70 grain Noslers?
I have not annealed the brass as it is new.
I do remember reading that a very fast powder and long bullets should be used (I have a few pounds of benchmark)

Provided your chamber is cut correctly and the factory brass is a "crush" fit I would simply take your current load and shoot it. If the brass is tight in the chamber no reason seat the bullet in the lands.

For my .243AI I simply load some good accurate .243 full loads and go at it. Sort of trial and error, but very effective and provides for decent shooting while a pleasant side effect of creating usuable AI brass.

I would however be sure to have the bullet engage the rifling to hold the case back against the boltface during obturation.

If your rifle is chambered correctly, there is no need to seat the bullets out against the lands. The bolt will close with a "crush fit".

What eddie said .
Used 42.5 gns Varget and the 70 Nosler in mine . Stiff loads give nice sharp shoulders .