Not much on the extractor/spring setup. Get a good spring kit and replace every 2500 rounds on a carbine system. Rifle and mid length can go longer but at $5 a kit why?
There is a lot of confusion on which gets what. I use BCM's 5 coil kit but I leave out the o-ring on my mid length and intermediate. Too much extractor pressure can cause issues same as not enough.
The extractor needs to be sharp where it grabs the case. Replace every 5000 rounds or as needed. Again these aren't very expensive so get a good one. A Colt at Brownells is under $30 and is much better than the cheaper ones I've seen.
