[stagpanther]

Sounds like a magazine spring and anti-tilt follower issue to me if it only happens at the end of the stack. The cartridges may look like they're being pushed down--but it could also be they are wedged in such a way they won't release easily and pivot instead. If the magazine rattles around easily in the receiver's mag well, you might want to try putting some tape on the side of the magazine where it fits into the well--just to see if perhaps the closer mag walls take away that last rounds issue. Otherwise I'd suggest trying a 5 and 10 round mag to see if the same problem happens.