Aero quantum 308 handguard issue

Got kind if a weird one here. I have a 308 that is a 2a xanthis upper, faxon lightweight barrel and I'm trying to put a quantum handguard on it. When I hand tighten the barrel nut it lines up perfectly with the gas tube hole (nut has 4 slots for gas tube). When I got to wrench it I can only get it half way to the next one. If I try 1,2,3,4,5 or 6 shims it always lines up the exact same place. The shims end up embedding in the nut against the shelf so it's definitely coming in contact with them after I slide them on the barrel. What the heck could be causing this?

Two problems by the way. One, the nut isnt tight enough when I hand tighten (obviously) and wrenching goes too far and not far enough. Second, even if it was tight enough by hand the handguard when slid on doesnt quite contact the receiver like it should.