Lapping upper receiver or use shims timing barrel nut ?

While installing my hand guard on a recent build, adding and installing shims to get barrel nut timing correct. A thought came to me that the lapping I did changed the amount of shims I would need. I only lapped enough to get surface square. But would it be wise to lap enough to where you don't need shims if you only need to take say .006" to get proper timing. With some hand guards I think you would get a better fit on the top rail. Also your feed ramp would have a better transition from upper to barrel if that needed correcting.

Doing more work to achieve a little more accuracy is well worth it to me.

I'm no gunsmith but at some point barrel setback would seem to become an issue. It will affect the position of the bolt carrier in the upper receiver.
How much setback is to much is the question.

Using different amounts of torque or setting back the barrel nut surface would be a better solution I would think. That would not affect any internal components.

.006” is a lot; only take enough to square the face.

Definitely shims.  Real easy to do more harm than good with a lapping tool.

You shouldn't need either. I can't think of a rail system out there where the barrel nut needs to be clocked in one position (usually there's like ~60? to choose from).

Any barrel nut that can be installed with the standard wrench has 20 scallops/holes, so one every 18 degrees.  Still, I've yet to encounter one that didn't align between 30-80 ft lbs.

A few proprietary designs, like the UTG Pro SS, offer extremely flexible indexing on account of the gas tube needn't be involved in alignment.

 

I guess I was way off in my estimation . But I do agree that with the flexibility of 30-80 ft lbs, shimming shouldn't be needed.

.006 is a bunch to take off. I only take enough off to square things up, and you can see it happening by checking often and watching the finish. Once it is just to the point it is all silver it is good. I check my barrel nut and see if I need any more off to get mine at right around 65 pounds. It usually does not take much more to get it where I like it. Nothing close to .006. I go so far as to rocksett my barrel to the upper receiver as well before I tighten the barrel nut for the last time. Is it worth it? Probably not, but I like to do anything I can to take out variables in the upper assembly.

Shouldn't need to remove near that to gain a few degrees of nut rotation.  Be sure you lubed the nut and go on and off a couple of times before going full torque.  Should get  you there without issue.