Failure to extract on new build ***Fixed-update on first post***

[MJDGator]

So I have completed a 300blk build. I took it to the range and I am having extraction issues. I have tried a couple of things to troubleshoot but all combos have resulted with the exact same result. I load 1 round in a mag, seat the mag and release the bolt, pull the trigger and the gun fires, bolt locks back, spent casing is left in the chamber. If I let the bolt forward gently and push it home with the forward assist then pull back the charging handle the spent case comes out pretty easily. Also if I load a round then pull back the charging handle without firing it the round comes out as easy as you would expect it to.

So far I have tried the following variations with 2 types of ammo (Fiocchi 150gr FMJ, Remington 125gr Match):
2 different BCG's: Wilson Combat 5.56 NP3 and a LaRue 5.56 BCG
2 buffer weights: A5H1 and A5H2 - bolt locked back every time for both buffers

Additional setup info: Ballistic Advantage 8.3" 300blk barrel, BCM intermediate A5 buffer tube w/Sprinco green spring, BCM Blem upper, EFAB muzzle brake, no suppressor and no subsonic ammo has been used.

Looking at the spent casings I not see any gouges from the extractors nor do I see brass shavings on either bolt face. Any other trouble shooting ideas? Neither extractor has a crane o ring and I would prefer to get the rifle working without one.

I have contacted Clint with BA and he is helping me but I figured that I would also check here and see if anyone else has had similar issues and how they fixed it.

***Fixed - Gun Running great***

I got the barrel back from Ballistic Advantage. They ran my barrel with my bolt and a few other bolts in the shop. They said it ran fine for them but decided to send me a new barrel. I have installed the new barrel and made it to the range today. Everything ran great with the A5H2 weight buffer and the crane o-ring on the extractor spring. No marks on the brass at all. For kicks I disassembled the bolt and removed the o-ring. That caused failure to ejects with the spent case laying loose on top of the magazine. So coupling that with the fact that BCM recommends using the o-ring on their site for 300blk and AAC sending their bolts out with the o-ring I guess it is not unusual to need them. I may try to increase the weight of the buffer and see what happens as the bolt locked back every time on an empty mag. Beyond that I am calling it good to go. As far as ejection of the brass they were bouncing off the stall divider and piling up right by my feet.

[Edgethane]

Cycling by hand isn't as violent an operation as cycling by firing.

The extractor isn't holding the case rim tightly enough during firing. When the case is extracted far enough be ejected, the ejector is actually pushing the case over the extractor claw.

Either the extractor claw is out of spec, or the spring isn't doing the job.

Does the extractor have, at least, an "insert" inside the spring? This might be enough added tension to make things work. I'd also closely inspect the extractor, comparing it to examples known to work properly.

I have never had to use a 'donut' on any AR system I've worked on, and that includes MK-18s and HK416s. The spring insert was sufficient.

[MJDGator]

Yes the extractor has a black insert in the spring. The claw looks ok to me comparing it to another one that has functioned flawlessly for about 1,000 rounds in a 5.56 rifle...I even tried that one in this gun but it produced that same results.

Interestingly enough...just browsed BCM's 300blk barrels on their site and they state that they recommend using the crane o-ring with the 300 blackout. I may order one of their extractor enhancement packages and give that a shot. First with just the insert and spring to see if that is enough and if not then the o-ring.

[Edgethane]

Sounds like you've done your homework.

I'd go ahead with your plan. Please give an update on your progress.

[26 Inf]

I don't know that I would go out and buy one, but I'd try the A5H3 buffer if I could borrow one, the extra .7 oz might slow stuff down enough that the case will have contracted and extract. Like I said, I'd try to borrow one to see how it works. Of course the H3 almost certainly will give you problems with subsonic ammo.

Most likely if you put the donut on it will extract okay.

Too bad you didn't fire any subsonic out of it to check extraction.

[P2000]

I wonder if this is a rough or out of spec chamber?
It seems you have done all of the reasonable troubleshooting by using 2 different known good BCG's.

Keep us posted please, I'm curious.

[MJDGator]

Thanks. I will update the progress. As a side note, Clint from Ballistic Advantage contacted me again and is offering to trouble shoot my upper. I just need to send it to him and he said he will get it working. If it has anything to do with the chamber/barrel he will replace it and refund my shipping expenses. But I really doubt that is the issue.

So my plan is to try the BCM extractor upgrade kit and then if that does not work I will take Clint up on his offer. Of course wouldn't you know I just ordered some stuff from BCM a few days ago.

[MJDGator]

I wonder if this is a rough or out of spec chamber?
It seems you have done all of the reasonable troubleshooting by using 2 different known good BCG's.

Keep us posted please, I'm curious.

Yeah that is what I was thinking at first but now I am not sure. If I separate the upper from the lower and drop a Remington round into the chamber and push it down with my finger it will drop right back out when I point the barrel up. The Fiocchi rounds I noticed that the last 1/8" or so snugs up in the chamber and I have to point the barrel up and bang the upper on my hand and they will drop out after a few hits. Of course I have not cleaned the gun after the range so there is probably a little carbon in there. I colored one of the Fiocchi rounds with a black marker and dropped it in the chamber then pulled it out. I did not see any clearly defined scratches or scuff marks on the case.

As for the buffer weight that is something I may try if the BCM kit does not work. Right now all I have is a A5H1 but I mentioned an A5H2 because I cannibalized a tungsten weight from a spare H2 buffer that I have. So I can always take another tungsten weight from the H2 to create an A5H3.

I never considered trying subsonic rounds...thats a good idea. I guess that would be sort of similar to going up in buffer weight.

[Iraqgunz]

Sounds like a chamber issue. Remember hand cycling won't give the same results. The casing heats and expands within the chamber.

[Clint]

Yes the extractor has a black insert in the spring. The claw looks ok to me comparing it to another one that has functioned flawlessly for about 1,000 rounds in a 5.56 rifle...I even tried that one in this gun but it produced that same results.

Interestingly enough...just browsed BCM's 300blk barrels on their site and they state that they recommend using the crane o-ring with the 300 blackout. I may order one of their extractor enhancement packages and give that a shot. First with just the insert and spring to see if that is enough and if not then the o-ring.

So my plan is to try the BCM extractor upgrade kit...

It appears you're not the only one with 300 BLK extraction issues.

https://www.m4carbine.net/showthread...e-unsuppressed

http://www.300blktalk.com/forum/viewtopic.php?t=80046

Putting it all together, AAC, Noveske and BCM all recommend using a high power extractor and heavy buffer in the 300 blk.

This leads me to believe that, for whatever reason, 300 BLK pistol barrels generally don't extract that easily and in many cases require a stronger extractor and heavy buffer (slowing extraction) to be reliable.