The remarks about the weak magazine spring are correct. However, I respectfully disagree with the feed lips holding the round too long, (thus causing the nose dive). The nose dive occurs long before the rear of the round ever leaves the feed lips; whether short or long feed lips are involved.
If the feed lips are opened up too much, they can allow the feeding round to "stand up", after the initial nose dive is turned back up toward the chamber by a proper feed ramp.
If the feed lips are too long, and are indeed "holding the round too long", then you have the possibility of a "nose-up-angle-jam" because the rear of the round was not released in time to slide up the breach face. (Don't mistake this with angle-jams that occur because of excessive extractor spring tension).
Building on a previous post... if you can find a magazine with feed lips that were hand worked by the former Seattle/Bellevue Detonics gunsmith, (a man who repaired over 2,000 Detonics 45's between 1977 and 1986), you can make some headway troubleshooting this problem. This guy currently works at Wade's Eastside Gun Shop in Bellevue, Wa. (425) 649-5995.