Hanging up a half inch before lockup is an indication of an extractor issue.
The base of the cartridge case has to slide up the breach face and underneath the extractor hook as the cartridge is being pushed out of the magazine. If the extractor is improperly adjusted or clocked, the case rim cannot slide into place.
It would take some eyes-on troubleshooting, but I'd bet installing a quality extractor and over-sized firing pin stop (to prevent extractor clocking) would cure the feed issue.
Another thing to look for is a burr around the firing pin hole in the breach face. A rare possibility is the firing pin being stuck so that the tip sticks out of the bolt face.
Last edited by DnPRK; June 6, 2012 at 07:45 PM.