New Upper Build Locking Up After Firing

[montana]

From my experience, and from what he said was the issue, the extraction cycle had started, but was incomplete, and then the buffer spring closes the bolt back up on the slightly expanded round. I've seen this quite a bit when adjusting gas blocks, especially on larger rounds. A better way to remove it than pounding on your charging handle is to take a small flat screwdriver, or even a longish allen wrench, and use it as a lever through the ejection port, in front of the carrier and gently pry it back. This works pretty easily usually.

Makes sense.