On the left is an older worn unknown brand AR15 extractor. Note the chips on the groove where it holds a case rim. The extractor spring has a blue insert. It’s replacement on the right has a black extractor insert, and an O-ring. The rifle the old extractor was pulled out of was having some extraction issues. The new extractor should put an end to those issues.
The M16 used a blue extractor insert and a 3 coil spring. Later a 4 coil spring and harder black insert was adopted. Sadly some companies have produced blue strength inserts in both blue and black. Bravo Company’s Paul Buffoni has said that the durometer measurement of the blue insert is 60, and 80 for the black insert. This shows that the black insert is harder.
Now there are 5 coil springs. When purchasing new extractor springs for a carbine, I would recommend buying the new 5 coil springs. The additional O-Rings and D-Fender rings are generally not necessary, but they can aid in extraction if you are having issues.
Scattered Shots 
One thing about extractors is that the edge of the extractor (the rear face, inside radius edge) needs to be sharp, not broken down. The extractor on the left has been broken down, and added/replacement springs won’t help that much. The extractor on the right has a slight break on the edge, and could be sharper.
This is where I advise people to look at the Mauser 98 claw extractor. Look at the angles, the sharpness of certain edges, and then look at the way it is held onto the bolt. The clip that goes into the groove right behind the bolt lugs, and that groove, are machined with bevels to pull the extractor more tightly into the axis of the bolt the harder the bolt is pulled back, thereby removing the need for adding more and more spring pressure.
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