Hey ya'll, I got the BCG that I ordered from Bravo Co, today.  In the package was this little rubber gasketish thing about the size of the gas tube.  A document labels it 'Mil-Spec Crane O-ring...  What is that for.  I had an M-16 in the military, and I don't ever remember having a rubber o-ring in there.  Or did I just not get deep enough in there to find it?  Or is it unnecessary.  What is it it for?  Any help is greatly appreciated.

~Robert

It goes under the extractor if needed. Leave it out unless you're having a problem extracting casings. Actually BCM may install these from the factory and it could be a spare but I'm thinking not.

Ok.  So if the extractor doesn't do it's job well, that can be used to improve it's performance?

Yes, well kind of, the O-Ring is an after thought that solves FTE problems. In a combat rifle it can be looked at as cheap insurance. BCM makes top notch products. Theirs would no doubt work well either way. The O-Ring will increase the pressure that the extractor puts on the case. This is often desirable with one exception that I can think of and that is if you happen to reload. The O-Ring does tend to mangle the base of the case, I should say the ones I've used and seen.

O-Rings were designed to be installed in rifles that absolutely have to get the job done and reloading isn't really a consideration. Most BCG's in most rifles will run just fine without them being installed, others hiccup occasionally. I looked at BCM's site and it says that their BCG comes with a Crane O-Ring but having never owned one, I can't honestly tell you if it comes installed. I know that other manufacturers include one with their product but don't initially install it, BushMaster used to do this, I believe S&W does this currently. You could call them or better yet go shoot it. If it runs well and either doesn't cause the problem I mentioned or concern you leave it as is. BCM uses an upgraded extractor spring and the proper extractor spring buffer (black). These two items by themselves will all but guarantee that you won't have a problem with or without the O-Ring. There are of course other problems that will cause FTE problems, short stroking (several causes) for instance. If this happened to be the problem there are other details that can be used to help run down these type problems.

That was awesome info.  Well, if the stock ever gets here, I'll put it together and try it out.  Thanks for the detail!

I'm glad you found it helpful.

Don't run it if you dont need it . It will chew up brass pretty good. I installed mine thinking no big deal since it was included . My first cleaning job was fun removing tiny bits of brass from my reciever. They do extract the hell out of rounds though ,if you ever have problems.