SBR issues, opinions needed.

[bkjeffrey]

I didnt know where to put this, NFA or gunsmithing, please move if necessary.

I recently built a 7" AR15 SBR . I used a standard midwest industries low profile gas block and pistol gas tube. Has a standard Bushmaster bolt carrier group as well.

When I first test fired it I went through about 120 rounds of LC M885 ammo and it ran fine. I took it home and cleaned it and put it away.

Today I went to the range and every single round I fired would not extract. The bolt would cycle, feed a new round from the mag and jam up because the previousley fired cartridge was still in the chamber.

I could drop the mag, clear the jam and send the bolt home and it would extract and eject the stuck case just fine when I cycled the action by hand.

The fired rounds that were stuck in the chamber were inspected and there are no signs of the extractor peeling the lip off of the brass.

I am going to replace the extarctor and extractor spring anyway.

Are there any other schools of thought as to why a 7" SBR AR15 would do this?

 

[surbat6]

Sounds like your extraction problem is unrelated to the 7 inch barrel length. I agree with replacing the defective parts. If I were in your situation, I'd go with at least a new extractor spring after inspecting the extractor itself for damage.
Did you check the chamber for roughness or damage? That would also hinder extraction.

 

[taliv]

get a bravo company bolt upgrade kit. it has a better extractor, spring, insert and o-ring. i'd say 90% chance that solves your problem.

 

[grog18b]

Agree, your extractor system is malfunctioning. The "D-fender" works well, as well as a simple "O" ring around the extractor spring can fix your problem. Let us know how it goes. GROG

 

[BikerBen4]

I would say that it could be over-gassed, meaning the gas port in the barrel is larger than it should be, sending too much gas into the receiver. That problem could easily result in the bolt slipping right off the back of the case.

Just a thought...

 

[DoubleTapDrew]

I'd try this first, hopefully it'll do the trick and it's a whopping $5
http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm

 

[bkjeffrey]

Ok, I fixed it and I hope this may help someone in the future.....

I bought this from Midway: AR-Stoner Heavy Duty Extractor Upgrade Kit $21.99
Product #: 745270

and added a D-Fender D-ring.

The gun runs like a Ferrari now! For S&G I tried swapping to an H buffer and the gun short cycled on me a couple times. So, standard CAR buffer with a heavy duty extractor seems to be the ticket for my SBR. If the H buffer caused short cycles I assume that the gun is not "over-gassed".

 

[strambo]

It's interesting that an H buffer would cause it to short stroke...in my limited knowledge, I would assume it isn't over gassed as well. Standard action spring (not Xtra power) and is it a SA or FA carrier?

 

[bkjeffrey]

No extra power recoil spring