Stupid BCG Question

dkf · 02-14-2013, 11:28

Got my BCM BCG and it comes with a small o-ring. What exactly is it for? A "Crane O-Ring" of the extractor?

WoodenPlank · 02-14-2013, 11:30

Yes, that's the Crane o-ring. If you are having extraction issues (ie: extractor slipping off the rim of the casing too early during cycling) the o-ring gives extra tension on the extractor.

F_G · 02-14-2013, 11:32

I have 4 BCM BCG's and they came with the "O" ring already installed plus an extra in a small sealed plastic bag, I'm guessing that's a spare they sent along.

dkf · 02-14-2013, 11:33

So just leave it off unless I have issues? Going in a mid length upper.

dkf · 02-14-2013, 11:36

Quote:

Originally Posted by F_G

I have 4 BCM BCG's and they came with the "O" ring already installed plus an extra in a small sealed plastic bag, I'm guessing that's a spare they sent along.

Ok. I took the BCG apart to clean and reoil but did not remove the extractor. I'll just hold onto the o-ring.

WoodenPlank · 02-14-2013, 11:41

Quote:

Originally Posted by dkf

So just leave it off unless I have issues? Going in a mid length upper.

Yep!

fuzzy03cls · 02-14-2013, 13:36

None of my BCM's had the o ring pre installed?

Quote:

So just leave it off unless I have issues?

Basically. I added it on a few, & really see no difference other then trying to get the damn pin back into the extractor pin hole. PITA with the o-ring installed.

dkf · 02-14-2013, 14:48

Well maybe I will strip the bolt down again and see if the o-ring is installed on it.

dkf · 02-14-2013, 22:19

Tore the bolt down again. No o-ring from the factory.

Warp · 02-15-2013, 08:33

I don't know anybody that uses the o-ring. Hold onto it, but don't worry about it and don't use it unless you have a specific problem that diagnosis indicates use of the o-ring for.

samuse · 02-15-2013, 20:42

You'll generally only need it in suppressed SBRs.

If you have a properly gassed mid length, you don't need it.

I run nothing but 14.5" and 16" carbines (Colts and 1 BCM) and I've never needed the O-ring.

humanguerrilla · 02-16-2013, 01:03

......

ottomatic · 02-21-2013, 20:19

Quote:

Originally Posted by samuse

You'll generally only need it in suppressed SBRs.

That is exactly what I am looking to (eventually) put together. Suddenly I am worried! Please tell me why I am possibly going to have extraction issues. BTW - no full auto and intend on going with an adjustable gasblock.

JimD303 · 02-21-2013, 21:53

I use them and recommend them in every configuration. They don't hurt anything and only add extractor tension... nothing wrong with that.

samuse · 02-22-2013, 10:15

Quote:

Originally Posted by ottomatic

That is exactly what I am looking to (eventually) put together. Suddenly I am worried! Please tell me why I am possibly going to have extraction issues. BTW - no full auto and intend on going with an adjustable gasblock.

Suppressed SBRs usually have much higher gas pressure in the chamber during unlocking/extraction. More extractor tension is beneficial because the case is actually being extracted before it fully contracts.

samuse · 02-22-2013, 10:17

Quote:

Originally Posted by JimD303

I use them and recommend them in every configuration. They don't hurt anything and only add extractor tension... nothing wrong with that.

If you don't need 'em, don't use 'em. The added tension can decrease the life of the extractor and the extractor pin and cause feed and ejection issues if the tension gets excessive enough.

I like running a black insert and a Colt gold spring in carbines and mids. The O-ring would be ok if you were running a rifle spring and a blue insert in a carbine or mid gas.