Having chased this ghost a few times in my life it was no surprise to again find it floating around AS this weekend.
Here is what happens. The magazine and bolt have an interference fit and this causes a bunch of friction and tons of stove pipe malfunctions. this can happen with any bolt, rifle, or magazine. The only fats cure is to swap mags out and get one that does not hit. The following is a pic from this weekend. If you ever have a rifle that wont behave no matter what you do this just might be whats wrong. The mag either has to be real dirty or you can color the feed lips with sharpie to see whats up.
(http://i8.photobucket.com/albums/a47/nemohunter/IMGP5822.jpg)
as you can see by the shiney spots this one was real bad.