Question about Crane O-ring...

[ANDROTAZ]

Sorry for the ignorance, fellas...I understand that the o-ring that comes with the BCM BCG is meant to enhance extraction, but how exactly is it installed? Also, how exactly does it aid in extraction? Thanks a lot.

[royta]

Sorry for the ignorance, fellas...I understand that the o-ring that comes with the BCM BCG is meant to enhance extraction, but how exactly is it installed? Also, how exactly does it aid in extraction? Thanks a lot.

The o-ring goes around the spring. It increases the spring pressure against the extractor. Through leverage, the extractor now grips the cartridge case harder.



If you don't mind, I'd also like to add to his question. Which length gas systems benefit from the enhanced extraction? I thought I read that mid-length or rifle length gas systems don't need extraction springs as strong as carbine length gas systems.

[Iraqgunz]

royta,

Generally they are recommended for carbine type weapons and more so when firing in full-auto.

[Eric]

Looks like this when installed.

[T-TAC]

This summer I completed a M-4 build. The top end came from M&A parts.
I would occasionaly get a faluire to extract. I took a look at the Bolt, the extractor could not even be pulled back away from the bolt with finger pressure. I noticed the extractor spring was the new Black bumper heavy spring. I replaced the spring with the standard spring with a blue bumper. I also changed the extractor, just in case that was out of spec. Problem solved. Another 400 rounds down the pipe and no bobbles at all.
I don't understand the need for the heavier spring, Much less the O ring.
Maybe if I was going to shoot a 6000 round course, But the gun has to run right out of the box or I can't bet my life on it.
Maybe changing the extractor spring more often would be a better route.

[Iraqgunz]

A few observations. You do understand that all weapons have a break in period? You have changed the extractor spring and insert and it works for you, but there is a reason why the M4 has such a stout spring. If you were firing in auto mode you would find out.

Another thing to consider is that you as an individual can change springs and insert like underwear. For the .MIL, .GOV or contractors that have hundreds or even thousands of weapons it is a cost issue.

Not every mod that the military does has a direct need in the civilian world. I use the O-ring and MIL extractor spring and inserts on my weapons at home and have no issues at all.

This summer I completed a M-4 build. The top end came from M&A parts.
I would occasionaly get a faluire to extract. I took a look at the Bolt, the extractor could not even be pulled back away from the bolt with finger pressure. I noticed the extractor spring was the new Black bumper heavy spring. I replaced the spring with the standard spring with a blue bumper. I also changed the extractor, just in case that was out of spec. Problem solved. Another 400 rounds down the pipe and no bobbles at all.
I don't understand the need for the heavier spring, Much less the O ring.
Maybe if I was going to shoot a 6000 round course, But the gun has to run right out of the box or I can't bet my life on it.
Maybe changing the extractor spring more often would be a better route.

[toddackerman]

FWIW...LMT recommends just a Mil Spec spring. black buffer an NO O ing for a mid length system. When the O Ring came out I had several failures to extract on my LMT MRP 16" Middy until I took out the O ring. And of course...I never had any issues to begin with!