For the most part, tuning an AR with an adjustable gas block is pretty straight forward, but there can be complications from unexpected sources. Not because it's rocket science. Firearms actually are rocket science since firearms accelerate a payload into a ballistic arc using a solid fuel rocket engine, but it's primitive rocket science and simple to use. Complications usually arise from mechanical sources and are usually easy to find and fix. Usually.
Troubleshooting is often complicated by several factors. First, the problem starts off by being intermittent. It shows up only occasionally and often only when another intermittent variable is introduced.
Second, when troubleshooting, it's human nature to follow "If/Then" thinking, even when it doesn't always make sense. For example, if there is a problem with ejection that is resolved by cleaning and lubing (go with the simplest solution first), then the problem must be that whenever the problem arises, it must be because the rifle needs to be cleaned and lubed. What is missed in this case, is the fact that the real source of the problem is that the extractor spring or perhaps the ejector spring is starting to fail.
Third, is the very human tendency to fixate on the current problem to the point of thinking it's the only problem. It was this type of thinking coupled with inexperience that complicated tuning the Wolf Pup, my AR pistol with a 10.5" Odin Works barrel. The gas port of the barrel is about .083" and over-gassed. An SLR adjustable gas block and an H buffer was installed which solved the over-gassing problem. But I was still getting the occasional failure to eject, resulting in an empty being left in the action while the bolt tried to strip a fresh cartridge from the magazine. Opening the gas block ended the problem for awhile. If opening the gas block resulted in improved ejection, then the malfunction was due to under-gassing. Cleaning and lubing also improved ejection. For awhile. This cycle kept repeating itself. There would be a failure to eject and I'd clean and lube or open up the gas block and the problem would go away. Until it came back.
It wasn't until I set aside all preconceived notions and looked at the problem with new eyes that I realized the malfunction wasn't due to a dirty AR or poor gas flow. It had to be something else. Investigation led to the conclusion that my problems were due a failing extractor spring. Once the spring was replaced, tuning became a snap and the Wolf Pup stayed tuned.
I recently received a tax stamp for my Omega silencer (Yay! Happy Birthday to ME!). I immediately installed it on the Wolf Pup and headed off to the range, confident that tuning it with the adjustable gas block would be a snap. It wasn't. I could not find a setting that would result in the bolt locking back on an empty mag reliably with the silencer installed. After verifying the AR would lock back on an empty mag reliably, I loaded one round in the mag, shoot and keep opening up the gas block until I got lock back. Trouble is, it would not lock back every time. It was frustrating because the gas block was open even more than it was unsuppressed. After opening up and closing down the gas block, checking for leaks and the inevitable cleaning and lubing, I stopped, cleared my head and looked at the problem anew. Although the BHO worked reliably when manually working the action, I noticed it had more play than usual. I replaced the BHO and the pin. With that done, it only took three or four rounds to get the Wolf Pup tuned and with the block closed down much more than it was unsuppressed.
The experience (re)taught me a couple of lessons. One, intermittent problems are caused by something that's beginning to fail. While the problem may clear up with cleaning and lubing (because we start with the simplest solution) it's only a matter of time before the problem returns. Two, certain mechanical problems are always caused by the same failing parts, no matter what If/Then thinking concludes. If/Then thinking needs to be based on facts to keep it from being misleading. Three, start troubleshooting without any preconceived notions. Focus on the malfunction and don't take shortcuts or get fixated. That only wastes time and effort. Four, attempting to tune an AR (or any other machine) with out of spec parts is an exercise in futility. If it cannot be tuned, look for what is out of spec and fix that first
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