Problems with Fail Zero bolt

[PistolPete]

I've got a buddy who is putting together a SBR and we got to test fire it last night. Since he didn't want to skimp he went with a Fail Zero bolt, bolt carrier group and hammer. He's running it in a BCM 11.5" upper on a RRA lower. And it jams. A lot.

He was getting failures to extract every 5 or 6 shots. The empty would come most of the way out and the new round would wedge against it trying to chamber. It's an easy enough malf to clear, but he was quite unhappy.

I sprayed it down with some CLP and that didn't help. I swapped his H buffer for an H2 I had, no help either. I swapped in a BCM bolt and carrier and it ran like a top. I put his Fail Zero bolt in my gun (12.5" BCM with a can on the end) and it ran like a top as well. I shot about 50 rounds with his bolt, no problems. He fired two full mags with my bolt, no problems. Fail Zero bolt back in his gun and it was a jam-o-matic.

Any thoughts? I'd like to think maybe it's a problem that'll go away over time, perhaps the FZ bolt is a touch bigger and dragging or something? We were going to play with more part swaps but ran out of time.

[Regular Guy]

My thoughts are it's under gassed. I'd plug the chamber and blow air through the barrel. That should let you know if the gas system has leak or the gas block isn't over the hole on the barrel. Next thing is the chamber maybe too tight. Try running some steel through the gun. I had to do that with my PSA lightweight.

Some gas blocks I've come to find out aren't always drilled right and just slapping them on will not work. You'll need to move it around to get optimal gas flow. I had to do this with my Grendel. There was quite a bit of space between the retaining ring and the gas block.

Is it stiff when you're charging it? That may indicate poor mating of parts.

Edit: Did his gun run with the BCM bolt?

[AKFTW]

My thoughts are it's under gassed. I'd plug the chamber and blow air through the barrel. That should let you know if the gas system has leak or the gas block isn't over the hole on the barrel. Next thing is the chamber maybe too tight. Try running some steel through the gun. I had to do that with my PSA lightweight.

Some gas blocks I've come to find out aren't always drilled right and just slapping them on will not work. You'll need to move it around to get optimal gas flow. I had to do this with my Grendel. There was quite a bit of space between the retaining ring and the gas block.

Is it stiff when you're charging it? That may indicate poor mating of parts.

Edit: Did his gun run with the BCM bolt?

I swapped in a BCM bolt and carrier and it ran like a top.

Sounds like it to me.

[TheLastOne]

aren't failzero's the coated NiBx stuff? As in, extra layer of stuff on there, that might be just enough to be ~too tight? My half assed guess is it just needs a little breaking in...

[PistolPete]

Yeah, I was thinking it was a gas problem until it ran fine with another bolt and his FZ bolt ran fine in my gun. Perhaps it just does need worn in.

Why did you suggest steel cased ammo, btw?

And I didn't say, but we were using mixed vintage PMC ammo. Some of the more recent stuff and some of the older stuff that has the sealed primers that seems to be a little hotter. Or at least make more fire at the muzzle.

[Regular Guy]

I suggested steel because its softer than brass and poly is slicker than brass. I've found only by trial and error if the chamber is too tight but has a good gas system that if will run steel. I have no massive pool of data but its worked a few times already.

Edit: Is the gas key tight on the FZ bolt? Does it have 3 gas rings? Does it pass the gas ring test?

[Braxton]

I suggested steel because its softer than brass and poly is slicker than brass. I've found only by trial and error if the chamber is too tight but has a good gas system that if will run steel. I have no massive pool of data but its worked a few times already.

This. I only run crap ammo in my guns, The thought being that if it runs Wolf it will eat anything.

[Unorthodox]

You said you shot the FZ Carrier with a can on the end and it ran no problem. Something with the coating might have fucked with the FZ Carrier enough to restrict gas flow. The extra gas pushed back into the system from the can may have been enough to work the action. Try running the FZ bolt in your gun without a can and see if it gives you the same problems.

Then swap out the FZ Carrier with a known good (Keep the FZ Bolt) and see if that runs. At that point you will know if its the Carrier causing you issues.

[rhi]

aren't failzero's the coated NiBx stuff? As in, extra layer of stuff on there, that might be just enough to be ~too tight? My half assed guess is it just needs a little breaking in...

My guess as well. I'm certainly no AR expert, but I know a thing or two about electoplating and metal finishing. Might be that the FZ BCG is a little high on the Nickel-Boron plating thickness (which is what I think they're using) and the upper is a little high on anodize thickness. Between the two, the plating on the BCG will win and wear-in the upper. Tolerance stackup.

If that's the case,simply cycling the bolt repetitively might fix it.

[RickOShea]

Just curious. Did your buddy get the semi or auto FZ BCG?

[Dave_M]

Guys, this is not a gas issue, it's an extraction issue--this is why it ran with the BCM bolt...

Upgraded extractor spring and O-ring should do it.

He was getting failures to extract every 5 or 6 shots. The empty would come most of the way out and the new round would wedge against it trying to chamber. It's an easy enough malf to clear, but he was quite unhappy.

This is often called a, 'false double feed'. It means not enough extractor tension.

FZ BCG's don't come standard with O-rings. BCM's do; that's why it ran with the BCM bolt and not with the factory FZ one.

ETA: Holy fuck this thread looks like Arfcomm I swear...

[Nightwing]

And Dave to the rescue.....

[Unorthodox]

zap

[Xframe]

My confusion is if the FailZero Bolt (and consequently the lack of Upgraded Spring/O-Ring) is the cause then why would said Bolt work in a gun where the only difference is the Can?

This is my confusion too. A can increases the gas, which is why a can will increase the cyclic rate. When the cyclic rate increases, the bolt carrier group velocity increases, and the energy of the bcg increases along with the velocity. The case wasn't being pulled all the way out of the chamber, which implies that there wasn't enough energy to pull the case out of the chamber.

Either way, if you replace the spring and o-ring and it works, let us know. If the malfunction is still occurring, please let us know also.

I'm just going by the information that is given. Hard to diagnose a system over the internets anyway.

This also.

[Regular Guy]

Wow, for a $350 bcg and hammer I'd have thought they'd provide a 0.05$ o ring.

[PistolPete]

Thanks for the advice Dave. I've got an extra extractor spring and o-ring from BCM, I'll put those in his bolt and see how that works.

I'm not sure if it's the auto carrier or not, I think it may be. I didn't look closely at it.

Anyone paying $350 for the setup is getting ripped off, his cost just over $200. That's not much more than a BCM bolt and carrier.

[crypto]

Dave, when in the OP, it sure sounds like a short-stroking bolt to me, why do you think it's an extractor problem?

My first guess was going to be too much drag between the hammer and bolt carrier, which someone else mentioned.

[Bearcat]

Guys, this is not a gas issue, it's an extraction issue--this is why it ran with the BCM bolt...

Upgraded extractor spring and O-ring should do it.

He was getting failures to extract every 5 or 6 shots. The empty would come most of the way out and the new round would wedge against it trying to chamber. It's an easy enough malf to clear, but he was quite unhappy.

This is often called a, 'false double feed'. It means not enough extractor tension.

FZ BCG's don't come standard with O-rings. BCM's do; that's why it ran with the BCM bolt and not with the factory FZ one.

ETA: Holy fuck this thread looks like Arfcomm I swear...

Did you install an O-ring in yours or did you leave it factory?

[Dave_M]

Dave, when in the OP, it sure sounds like a short-stroking bolt to me, why do you think it's an extractor problem?

Well, firstly because of this:
He was getting failures to extract every 5 or 6 shots. The empty would come most of the way out and the new round would wedge against it trying to chamber. It's an easy enough malf to clear, but he was quite unhappy.

This is called a, 'false double feed' and is pretty much always an extraction problem. It especially crops up with SBR's (make rifles shorter than designed, run into new problems to fix). I've seen it on probably a dozen [new] SBR's.

Did you install an O-ring in yours or did you leave it factory?

Wow, for a $350 bcg and hammer I'd have thought they'd provide a 0.05$ o ring.

I installed both a new spring and an O-ring. FZ ships (or at least used to ship) with a standard spring /w Blue insert and no O-ring. The reason is that not every setup needs an improved spring/O-ring (and yes, too much extractor tension can cause problems too). Middies, for example, don't need O-rings. Rifle-lengths [generally] don't need either one. Hell, most carbines don't really need the double spring/O-ring configuration but a lot of SBR's do for a myriad of reasons (and even then it depends on the size of the gas port, the length of the barrel, muzzle devices, suppressors, and other factors)

[rhi]

Holy fuck this thread looks like Arfcomm I swear...

Aww, now that hurt.

I'm here to learn.

Pete: Please post up the results once you change extractors.

[Bearcat]

Did you install an O-ring in yours or did you leave it factory?

Wow, for a $350 bcg and hammer I'd have thought they'd provide a 0.05$ o ring.

I installed both a new spring and an O-ring. FZ ships (or at least used to ship) with a standard spring /w Blue insert and no O-ring. The reason is that not every setup needs an improved spring/O-ring (and yes, too much extractor tension can cause problems too). Middies, for example, don't need O-rings. Rifle-lengths [generally] don't need either one. Hell, most carbines don't really need the double spring/O-ring configuration but a lot of SBR's do for a myriad of reasons (and even then it depends on the size of the gas port, the length of the barrel, muzzle devices, suppressors, and other factors)

Thanks. I just checked mine and it came with a black insert and no o-ring for the record.

[Xframe]

Thanks for the clarification.

[PistolPete]

The extra power spring and o-ring were installed and it ran like a top, not a single malfunction. Thanks for the advice Dave.

[rhi]

Thanks for the update, Pete. Now we know what to look for with this type of malfunction.