Hi Radar, just noticed your post.
If you haven't got it running yet, you might actually take a look at the ejector, the little pin atop the right side of the bolt head, while you're hand cycling the weapon.
If the ejector in in the "rearward" position as the bolt moves forward, it can catch on the ejector plate as the bolt drives ahead, jamming the bolt. Cycling it slowly, or cocking back allows it to pass, once.
This seems to be an issue of individual bolts coupled to different receivers. I have several different bolts, and all the ejectors seem to be matched, or have worn themselves to match, their respective receiver/ejector plate combo.
And maybe just semis. Maybe the full-autos set up such severe vibration that the problem couldn't occur.
I had TNW convert my trigger and install the two rollers. It wasn't expensive. Would that be an upgrade to smooth out the system? Well, good luck with it......Phil