There is one step most people overlook. The gas tubes port is usually off. When you install the gas tube in the gas block remove the rear set screw, look down through the hole and make sure the gas tube is not covering any part of the port in the gas block. If it is that will disrupt the flow and cause issues.
One other thing we don't talk about much because most get butt hurt when someone suggest it. Hold the rifle firm to your shoulder. I saw a video of a guy shooting last week. The rifle had been checked more than a few times and works with one shooter but not the owner. When the owner was shooting he was trying to hold the stock off his shoulder with his left hand. Every time he fired the scope would move to the rear 1.5" easy. That will cause problems and give you "scope" eyebrow.
Thanks for the advice. I'll definitely look into the gas tube port. There's no worry the rifle wasn't secure against my shoulder.
And that's what I said. lol
Check your gas tube coming out of the gas block. I was having the same issues. I was getting to much gas leaking around the tube at the gas block. I pulled the gas block off and covered the port inside the gas black and blew on the end of the gas tube with my mouth and there was very little resistance. too much blow by. I degreased it and sealed around it with red loctite. Runs like a champ now. Something to look at anyway. Hope that helps.
I've only been shooting ARs fo a year, built two.
My second one the gas tub was a easy slip fit in the gasblock.
Thanks to all the good troubleshooting guides on this forum I knew to proactively seal this junction.
I hope to shoot it next weekend, and I'm happy to know that if I have undergassing this is one area I won't have to worry about.
The guys on this forum really are great and do an awesome job of walking folks through issues!