I recently reloaded some .308 rounds for a friend's M1A. The rounds were loaded with Winchester primers, 40.9 grains of IMR 4064, Sierra 165 gr. HPBT bullets, in once-fired Remington cases. Most would only chamber 2/3 of the way. I used RCBS FL sizer dies and checked the completed rounds with a Frankfort Arsenal Maximum Cartridge gauge. Several of the rounds would not chamber in the rifle. Most of the ones which did would not extract, even though they were not loaded "hot". What am I missing?

You may need to use a small base full length sizer. My friend has one of these rifles but we got lucky and a regular FL sizer works. Neck sized rounds will not. The brass may have too much memory and returns somewhat to a larger case size.

Definetly try a small base sizer die. Make sure the OAL isn't putting the bullet into the lands.