Extractor not climbing over the rim of the live round on loading.
Start with pulling the extractor off the bolt, and make sure that you don't have both a extractor tension spring and a O ring ring installed around the spring (should only have the spring, and no O ring).  with the extractor back on the bolt, hook a spent case on the extractor, and cam the ejector into the bolt face a few times to make sure it not binding in the bolt face channel.  The extractor should be spring tension'd on the high side, but should not be binding as it being driving in, or let back out.

With the upper shotgun open, look at the bottom of the barrel extension feed ramp center section, and make sure that its centered on the lower front tack down lug below (to make sure that the barrel extension is not rotated in the upper receiver).  Next take a look at the tip of the bolt catch, and make sure that the carrier is not tagging the hell out of the top of it when it moving forward and the catch is all the way down.

Carrier with key alone, dry fit them into the upper receiver to make sure that the gas tube is correctly aligned with the carrier key.


As for the last two, I need photos of the bolt face with extractor installed, and then a photo of the entry chamber radius cut to make sure that is rounded and not sharp.

If the chamber entry radius is sharped edge, it can cause a ammo drag on loading to slow the bolt way down, and if the extractor is out of spec, then it top raduis surface that the rim would normally ride down to push it out to allow the bolt to slip down it too far inward, then the round just slams into the outer edge of the extractor instead.  Hence the front radius section of the extractor should match up to the radius of the bolt face channel.

To and bottom left bolts, the extractor are correctly aligned, with the rest of the bolts and extractors, the radius section on the top of the bolt is too far inwards towards the center of the bolt to allow a rim to correctly push the extractor out to allow the rim slip past isntead.

And remember that the extractor does not slip over the rim until the bolt lugs start to enter the receiver extension lugs, hence the ar-15 does not control feed like a Mauser rifle (where the rim slip up in the extractor claw as it leaves the mag), but push feeds like a 700 rem instead (where the rim slips past the extractor on bolt lock up instead.