I am installing a new barrel for the first time.  I have read Kuleck's book & the section on eliminating drag on the gas tube & carrier key by tweaking the barrel nut.   Should I be trying to get a completely interference-free fit or is a slight amount tolerable?  Right now I can feel just the slightest catch when I slide the carrier in without the bolt, but it still operates with very little resistance.  Do I need to keep tinkering with it or should I call it good?  Also, the barrel nut lined up right at 35lbs on my torque wrench.  Should I go to the next scallop or is the low end of spec OK?
Thanks

If your barrel nut lined up first try at 35lbs leave it be, some folks don’t even use torque wrenches for barrel installs, myself included.

I ensure the barrel nut is aligned with the upper receiver gas tube hole and no side loads are on the gas tube causing it to sit crooked. I also ensure I don’t bend the gas tube during install. Using these methods I’ve never had problems with carrier/gas tube drag.

tag

Quoted: If your barrel nut lined up first try at 35lbs leave it be, some folks don’t even use torque wrenches for barrel installs, myself included. I ensure the barrel nut is aligned with the upper receiver gas tube hole and no side loads are on the gas tube causing it to sit crooked. I also ensure I don’t bend the gas tube during install. Using these methods I’ve never had problems with carrier/gas tube drag.

+1

If the gas tube isn't concentric with the key it will wear unevenly, causing a gas leak that may eventually lead to malfunctions.  Watch the gas tube as you push the stripped carrier home; there should be no detectable movement.  If that's not the case, gently bend the tube at the gas block to nudge it in the right direction.  With a new key and tube, there may be some slight drag until they break in.

An easy and fast to align the barrel nut with the hole in the receiver is as you get close insert a punch that just clears the hole in the receiver, weld spring and delta ring.  Let it lay there as you tighten the barrel nut.  Watch the punch as you turn the barrel nut and you will see it center itself over the barrel.  Move the punch back and forth a couple of times just to make sure the weld spring on the delta ring aren't giving you a false reading.  Fast and easy.