The round comes out of the mag, hits the feed ramp, then hits the small chamfer on the barrel prior to going into the chamber and flings up. You need to "throat" the bottom of the chamber a little. This allows the feed ramp to guide the bullet in the chamber without hitting the barrel. The head space being incorrect, or the mags sitting to high can cause incorrect ejecting.
If you have correctly converted mags or Colt mags, a feed block adjusted so the ejector is almost rubbing the bolt, the ejector bent to the right so it's almost rubbing the bolt, throat your barrel, and check the head space, I guarantee you 100% these 9mm uppers run. I can post pics tonight if anyone wants to see them.
50rnd dump of silver bear 147gr video of my M16 6" upper I made(was RRA 16")with UZI coastal can ,and ASA mag well adapter, I don't know the ugly over weight guy....
[url]http://users.zoominternet.net/~picplace/m169mmdrum.mov[/url]