Or perhaps put another more polite way, there are many wrong ways and there are some better ways and there may just be a couple of correct ways to properly torque up that pesky AR15 barrel. Read my post about grease or not to grease. No point repeating myself. Gentlemen, stop and just think for a few moments about what you are posting here and what bad things could happen to you.
Steel barrel. Aluminum upper receiver. The correct way to align that barrel nut if it does want to line up, (it never will at first) is to remove the barrel and slightly dress off the end of the upper receiver. Again, read the post in the grease or not to grease thread. This is easy and fun. If one takes the times and has the proper mental attitude on not wanting to blow off your face, then things are fine.
However, if one just wants to not learn and just do it any way, be politely advised that that course of action does lead to the rocks and reefs of potential destruction. Building AR15 riles is fun and easy. Building them correctly is a very good idea. The potential otherwise is not worth the risk. If anybody has any specific questions, please feel free to PEM. HB of CJ (old coot) Just passing it forward.
Forum acting up a bit. Dropping paragraphs and sentences some. The barrel extension is torqued up to around 80-90 pounds. The older barrel extensions had L.H. threads. The barrel gets torqued up to around 40-42 pounds. R.H. threads. Everything needs to go together correctly. We will leave pesky OEM iron site barrel indexing for another time, unless somebody wants to learn more.