Unusual 300blk FTE

[Superhero]

Ok before I go tearing everything apart I'll try it with a known good BCG and I'll try polishing the chamber.

Never polished a chamber before, about to google it but I'm open to any tips or advice!

[Superhero]

What should I be looking for in the extractor? What might be wrong with it? I've pulled it apart and looked at it closely. No marks, no burrs, nicely machined. It is identical to the extractor on another good BCG I have.

I think I’m this case the back pressure from the silencer is helping with extraction from back pressure.

I do not believe the gun is over gassed. I’d guess tight chamber but more likely the extractor itself.

[jackblack73]

It's really easy to try the o-ring, as long as you have one. You said it's a 9" BCM barrel. My 9" 300 BLK BCM upper came with an o-ring. My two other 5.56 BCMs didn't come with o-rings. To me that's a clue that they think it's necessary.

[Superhero]

That's an apt observation. Have you had any issues with your extractors breaking? That is a lot of tension.

It's really easy to try the o-ring, as long as you have one. You said it's a 9" BCM barrel. My 9" 300 BLK BCM upper came with an o-ring. My two other 5.56 BCMs didn't come with o-rings. To me that's a clue that they think it's necessary.

[MistWolf]

It's really easy to try the o-ring, as long as you have one. You said it's a 9" BCM barrel. My 9" 300 BLK BCM upper came with an o-ring. My two other 5.56 But is the best CMs didn't come wiccv C th o-rings. To me that's a clue that they think it's necessary.

Friends don’t let friends O ring. If the extractor spring needs an O ring to function reliably, the spring needs to be replaced.

Superhero, do the simple things first. Try a different BCG as Clint suggested. Do a lockback check to see if it’s under gassed.

The malfunction sounds like a bad extractor spring.

[bamashooter]

Ok before I go tearing everything apart I'll try it with a known good BCG and I'll try polishing the chamber.

Never polished a chamber before, about to google it but I'm open to any tips or advice!

The brass will likely appeared marred if it's the chamber. You're actually looking to only smooth the chamber; polishing not needed. One simple method I use:

Separate rcvrs and remove bcg

Get a .38 cal "mop" attachment for cleaning rod.

Install it and a length of rod to cordless drill.

Use a light abrasive like Flitz, automotive wheel polish, etc. Slather the mop well.

Insert into chamber and go to work.

Slowly worked in and out. Not so far out where paste is flying everywhere.

I usually go for about 45-60 seconds. Remove and reslather. Perhaps 4-5-6 times

Remove and clean well. Lightly lube.

Including cleanup and all, perhaps 15-20 minutes total taking your time. An abrasive toothpaste will work in a pinch.

[Todd.K]

The extractor has a bounce in the cycle, a difference in timing (like adding a suppressor) can make the difference in it coming back down on the rim or not.

Add extractor tension. O-Ring and standard extractor spring or an extra power extractor spring.

[Clint]

Todd,

when (in the cycle) does this extractor bounce occur and what causes it?

The extractor has a bounce in the cycle, a difference in timing (like adding a suppressor) can make the difference in it coming back down on the rim or not.

Add extractor tension. O-Ring and standard extractor spring or an extra power extractor spring.

[Todd.K]

It was in some military, Crane, or Arsenal report. I don’t recall it being specific on the cause, just that failed extraction wasn’t just the extractor slipping over the rim.

It showed that both the M16 and M4 did it but the timing difference made a malfunction much less likely in the M16.

[Disciple]

An interesting PowerPoint on extractor bounce.

http://www.dtic.mil/ndia/2003smallarms/din.ppt

The link is dead but the file is archived. https://web.archive.org/web/20161221...llarms/din.ppt