Broken Extractor

[monty]

Was ladder testing some 120 grain Gold Dots last week when I started to have extraction problems. After a couple of rounds not extracting properly, the rifle stopped extracting at all with a fired case stuck in the chamber. After getting home, I was able to easily push out the case with a wooden dowel.

I pulled the bcg and found the lip broken off of the extractor. This is one of the group buy bolts. Rifle has an 18" Faxon barrel with mid length gas. Roughly 600-800 rounds through it.

I ordered two new extractors from JSE Surplus and have them in hand. Was wondering if anyone has any clue why this extractor broke. Overgassed? Maybe just s--t happens?

Thanks for any help or suggestions.

Monty

[A5BLASTER]

Possible over gassed that and if the upper hasn't been lapped you should do so.

It will give the bolt a much more square surface to lock up and should extended the life of the bolt and extractor.

[southpaw]

After I installed my group bolt, my 12.5 pistol starting having intermittent fail to eject and weak ejection when it did eject. I replaced the ejector spring and beveled the end of the ejector, but that didn't help. I then noticed the fired brass had gouges from the extractor:

[ATTACH=CONFIG]15448[/ATTACH]

I beveled and polished the sharp corners of the extractor and that fixed the problem. I don't know if this is what caused your extractor to fail, but both bolts came from the same source.

This guys youtube video shows a similar issue and the solution:

[video=youtube;kMrMUyyWV0k]https://www.youtube.com/watch?v=kMrMUyyWV0k[/video]

[LRRPF52]

Tell us more about your 120gr Gold Dot load.

Especially with the 18" MLGS or 16" CLGS, you have to watch what you're doing with slower-burning powders or higher charge weights.

When the port pressure is high and you have a lot of gas feeding back into the BCG to initiate rearward momentum, it can be really hard on the bolt and extractor due to rotational torsion on the lugs and the extractor lip.

One way to combat this is to regulate the gas flow with adjustable gas.

Another is to regulate the carrier and buffer mass as a rate-reducer so the bolt stays locked longer. You can also add spring weight to resist early momentum from the gas system acting within the BCG.



The goal of both of these methods is to keep the bolt locked longer, allowing the chamber pressure to fully dissipate as much as possible before any rotational torsion is applied to the bolt and extractor, which are firmly in contact with the expanded case. We want as much case rebound as possible before primary extraction takes place. When you have a fully or mostly-obturated (expanded) case in the chamber and you try to pull it from the chamber with the extractor, the extractor or case rim often loses that battle and slips over or rips the rim out.

The worst case is the extractor failing entirely as you have here.

Did you measure your gas port by any chance? This dimension will also help paint the picture better.

What buffer and spring are you using?

[FLshooter]

Said you already had 600 to 800 rounds through the barrel. So I take it that the rifle was shooting fine up until you replaced the bolt?
If so, maybe it was just a faulty extractor. Check the spring when replacing.

[CJW]

Very interesting PF52.

[monty]

I did lap the upper before assembly.

For the Gold Dot load I was using Power Pro Varmint. Started at 25.6 gr and worked up. Had a split case at 25.8 gr. Split in the body of the case, but after looking closely, determined that the split was where there was a gouge in the case from an earlier loading, I believe caused by a magazine feed issue. At 26.4 gr is where the extractor issues started. Fired a couple that did not extract completely, the third did not extract at all. That is when I stopped.

I did not measure the gas port before assembly. Rifle has an H buffer (3.8 oz). Not sure on the spring, probably standard carbine spring.

Rifle had been shooting well before this issue came up.

[A5BLASTER]

I did lap the upper before assembly.

For the Gold Dot load I was using Power Pro Varmint. Started at 25.6 gr and worked up. Had a split case at 25.8 gr. Split in the body of the case, but after looking closely, determined that the split was where there was a gouge in the case from an earlier loading, I believe caused by a magazine feed issue. At 26.4 gr is where the extractor issues started. Fired a couple that did not extract completely, the third did not extract at all. That is when I stopped.

I did not measure the gas port before assembly. Rifle has an H buffer (3.8 oz). Not sure on the spring, probably standard carbine spring.

Rifle had been shooting well before this issue came up.

What's the jump for that bullet in your chamber?

[monty]

What's the jump for that bullet in your chamber?

Not sure. I will measure it and report back.

[Kswhitetails]

Congratulations monty! You've found the point in this particular recipe where the chamber pressure is still high enough during the early unlocking stage of BCG/Bolt movement that the friction of the case walls to the chamber walls exceeds the physical limits of your extractor. We call that success in destructive testing. Now, to change variables and continue, or to stop at 26 grains and call it good?

Have I missed resulting velocities? If you're not shooting over a chrony, you should be. Especially when pushing loads. You want to be watching for velocity spikes or dumps in conjunction with erratic ejection patterns like you've found here to tell you that you've found the limits of your barrel. In Grendel, things start to break before you find the typical case deformation signs. Velocity is the only early indicator you're getting close to danger. The good part of this is that the bolt or ejector fails before something even more catastrophic happens.

I have found "low nodes" for all three of my Grendels, and have to say, I've had a clam like permanent smile at the range. Predictable, shootable, and boring. But stacking slow projectiles at range has it's own charm; Mainly bragging rights. And equipment that never fails.

Are you wanting to make this your hunting load?

[monty]

I have a magnetospeed but was not using it for this test as it has been acting up.

Speer load data for this bullet lists 27.3 gr as max load, so I assumed it would be safe. Guess that is what I get for assuming.

I will try to finish this test using a chrono. Hopefully I can confirm or not that this load is too hot for my rifle. Was hoping to use this for hog and deer hunting. I have other powders (CFE or AA 2520) to try out if this does not work out.

[imaguy3]

Don't forget... extractor's can break other ways too.. not just the lip... This wasn't on a grendel, but it was on a properly gassed 5.56 and saw less than 1000 rounds before breaking. The gun never hiccuped.. I only noticed it during routine cleaning.

[A5BLASTER]

That is a good point. Sometimes things just fail. It could be from a bad heat treat or a defect in the metal itself.

Now if it continues to happen then it would be sage to say it's something with the rifle in question.

[imaguy3]

That is a good point. Sometimes things just fail. It could be from a bad heat treat or a defect in the metal itself.

Now if it continues to happen then it would be sage to say it's something with the rifle in question.

This gun has been in service since 2008... seen many thousands of rounds, this was the extractor that came on a new bcg that got thrown in last year. I think it was just a bunk part.

[A5BLASTER]

That is a good point. Sometimes things just fail. It could be from a bad heat treat or a defect in the metal itself.

Now if it continues to happen then it would be sage to say it's something with the rifle in question.[/QUOTE

This gun has been in service since 2008... seen many thousands of rounds, this was the extractor that came on a new bcg that got thrown in last year. I think it was just a bunk part.

Was just saying in general not specifically too your pic.

[monty]

That is a good point. Sometimes things just fail. It could be from a bad heat treat or a defect in the metal itself.

Now if it continues to happen then it would be sage to say it's something with the rifle in question.

This may be the case here. I'm inclined to believe that the charge was not too hot at 26.4 gr. Speer lists 27.3 gr as max load. And I watched a video on Johnny's reloading bench where he loaded PP Varmint with 120 gr ELD's up to 29 gr with no problems. Also with an 18" Faxon barrel. Sierra's load data lists 29.6 max charge of PP V with 120 gr bullets. I know there are many variables but should be in the ballpark.

I will continue testing this load using my chrono and hopefully find some answers.

[LRRPF52]

Maybe try putting an H2 buffer in it.

With the next extractors, look at the linked video and make sure your extractor lip corners are honed down to a curve, rather than a sharp edge.

That alone will mitigate extractor torsion effects to a large degree, since the corners are acting as levers when they bite into the soft brass case rim during locking and especially unlocking.

Broken extractors are a big problem with some CLGS 10" 5.56 guns for this reason (especially suppressed), because they have to make the port larger to run the guns reliable since there is nowhere near the ideal dwell time.

A MLGS 18" AR15 can be really hard on the bolt and extractor if the gas port is too large or whatever load you're using hits the gas port with more port pressure. This is one of the main reasons why they went with RLGS on the SPR uppers in .223 Wylde with a reflex-type suppressor that allows more gas expansion in the first chamber before hitting the baffle stack.