the failure to extract problem is that spent brass gets stuck in the chamber and the extractor slips off. the bolt then tries to feed another round... usually the tip of the bullet gets jammed between the rim of the stuck brass, and the mouth of the chamber. to clear it, i have to drop the mag, put my fingers up the mag well and flick the jammed round loose, it wont fall out just from shaking or smacking the rifle. then i recock the charging handle, and then manually pull on the charging handle to extract the spent round.
after i put an o-ring on the spring, and got a chamber brush, the rate of failure dropped a lot, but still occurs about 20% of the time.
i wasn't thinking that this damaged brass issue is related to the FTE, but i usually take those jammed rounds and put them back in the mag and try to feed them again because i dont see any noticable damage besides scratched copper on the jacket... maybe they got weakened from being slammed into the back of the spent round? that could explain the dented case, but what about the ripped neck one?