Re: Always FL size for a gas gun?
Always FL re-size for an autoloader.
Buy a .308 case gauge or I can almost guarantee that you will ruin more cases than you'll spend on the gauge, not to mention unproductive days at the range, banging on charging handles (under bumped), or wondering why you have flattened primers with your starting loads, poor accuracy, and case head separations (over bumped).
Test re-sized brass in your chamber.
With the gauge, and a re-sized case, you can determine what the rifles headspace requirements are.
In my experience:
THE SINGLE BIGGEST RELOADING ERROR is improperly re-sized brass.
You should nail it to within 0.005" or less.
No need for small base dies.