My guess: His forward action screw is too long. It is hitting the front of the bolt keeping it from turning all the way. Look into the chamber with a bright light to confirm. He can also check for witness marks/scratches on the bolt head where it might be contacting the action screw.
Solution: Check to see if the front and rear action screws were reversed. The shorter one goes in the forward hole. If this is not the problem, remove the offending action screw, cut or grind off the appropriate number of threads, clean up the edge of the cut and reinstall.
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