http://www.bravocompanyusa.com/BCM-14-5-Mid-Length-LIGHT-WEIGHT-Upper-Receiver-p/bcm-urg-mid-14lw.htm

 

What is a black extractor insert? I saw it's a super tiny donut looking thing that came with my BCM BCG... what does it do?

the black extractor insert denotes that it is a 5 coil spring vs the 4 coil this is a stiffer spring which causes the extractor to grab the rim better. There's already one on the extractor the one that came with it is a spare.

Oh, ok. Good!

To be more specific, the "extractor insert" is located UNDER your extractor. If you remove the extractor from the bolt, you will see it. Typically AR bolts have blue extractor inserts which denote a lower power spring. The vast majority of AR failures center around Bolt/Extractor issues and magazine feeding issues, the black extractor insert is a great way to make sure you have a low chance of extraction issues.

Took it apart today and it wasn't there. So it isn't a spare. However, BCM on their website says that the spring they use is strong enough that you don't really need to use the insert. YMMV.

Put it in anyway, can't hurt.

You guys are talking about two different things I think.

 

One of you is talking about the plastic cylinder inside the spring that sort of acts like a guide rod or dampener. This comes in two flavors, white and black. jstang is correct that black denotes a higher tension spring.

 

Devsadvocate is talking about an o-ring. This is not the same thing as above. In order to increase the spring tension, soe folks add an o-ring or d-ring to the outside of the spring which prevents it form compressing as much as it would without it. less compression = more tension. This was often done to white insert setups to prevent extractor malfunctions. Some people put them on springs with black inserts. In theory, black insert springs should have enough tension to not need it, but I've yet to see a rifle have problems due to running ablack insert and an o-ring/d-ring. Although it can in theory be an issue.