Three super easy step!

Step 1, Adjust your resizing die to do a full size.

Step 2, take the 308 and only resize it 3/4 to 7/8 and remove the case, wipe off the excess resizing lube off the neck and shoulders with your fingers.

Step 3, Now your ready for full length resizing the case and finishing the process as any 243 round such as trimming to length etc.

By the way, no fire forming is required, shoot the load you have been shooting. If using military cases like I do, reduce your charge by 2 grains and work back up due to the heavier cases thickness.

73's