I just purchased a bcm bcg and the bag has a small o -ring in the bag.
Sorry what is that for?
Goes on the extractor spring/insert.
No need to install it as the BCM 5 coil spring is very stiff.
C4
Thanks Grant,
incidentally box came in from you an hour ago so this is a bcg i purchased from you.
It’s for land fill.
Well fantastic! I at least made one customer happy today! 
C4
If you ship my quad rail today, you can make two happy. 