Broken extractor

[tucansam]

[ATTACH=CONFIG]13295[/ATTACH]

[ATTACH=CONFIG]13296[/ATTACH]

Got a Monster bolt from the Faxon 12" group buy a year or so ago, the original group buy, not any follow-up ones (in case it matters in terms of lot for the bolt parts etc)

First of all, I'm not blaming the extractor, at least not directly. 12" Faxon barrel, carbine buffer tube and spring, 9mm buffer, standard gas block, suppressor. With this setup, it runs hard and is really, REALLY overgassed. I have to wipe the bolt down and clean carbon every 30-40 rounds. Without the 9mm buffer, the gun ejected brass at 1-2 o'clock. With the 9mm buffer, 3-4 o'clock is the norm, and mostly 4 o'clock.

I have an adjustable gas block to install, to minimize gas, as the gun is only ever run suppressed. I'm hoping that someone here will tell me that the gun running hard can break extractors. I've probably put 200 rounds through it, prior to this issue.

I'd also love to heard how those of you who are running 12" suppressed guns have tamed the gun (buffer, spring, etc)

Thanks.

[A5BLASTER]

Nobody has to tell you that the gun running hard can and will break and extractor, you already know it does.

Adjustable gas block and keep on rocking that bad boy.

[imaguy3]

is it just me, or does that extractor look like a MIM part?

If so I'd say search for a solid extractor if that is mim...

I had a coworker bring me a SW bodyguard with a broken hammer once, it was also a MIM part :confused:

[imaguy3]

http://www.blackriflearms.com/-65-Grende...p_297.html

[VASCAR2]

Another source for extractors is Alexander Arms. I called to see about getting reduced shipping since I was only ordering two extractors. They gave me reduced shipping since it was going out in an envelope. If you order online you’ll get the higher priced shipping. I sometimes add extra magazines or other items to my cart to help off set high shipping cost from some vendors.


https://www.shopalexanderarms.com/Bolts_...bly_1.html

[tucansam]

Thanks fellas! I appreciate the education.

[LRRPF52]

I'm using Bootleg Adjustable Carrier and a Maxim tiny 2.9oz buffer that comes with their PDW brace, along with the extra power recoil spring.

What's your round count?

What suppressor?

[tucansam]

YHM Phantom Stainless on a QD mount. Round count is right around 200.

[LRRPF52]

I would go Bootleg, with an extra power action spring.

Dial the Bootleg down to the suppressed setting.

Stop using the 9mm blowback firearm buffer, and use a correct (normal) cascading dead-blow buffer in conjunction with the extra power action spring.

[tucansam]

What is a "cascading dead-blow" buffer? Is it like the endine, with the weights that move along a center post? Any any specific "extra power" buffer spring recommendations? I've never looked at them, but I assume there are various sorts and/or ratings, as with everything else in the "tune it yourself" world.

Thanks for the reply!

[Klem]

Don't know what a 'cascading' dead blow is but Enidine make hydraulic buffers. So it's a different system to moving weights. That thin rod is a piston.

The carbon you are cleaning in the action is no doubt because you have a suppressor. It's all coming back past the case as it unlocks (not the gas system). It will coat the top rounds in your mag and the spent cases will be filthy. Just the down-side of using a can and there's not much you can do about it. Changing the powder to something that burns cleaner will help. If the action is unlocking early while there's still too much pressure in the barrel then this will make it worse by forcing the soot back into the receiver and your face.

The extractor claw may have broken because the case is still gripping the chamber making for more resistance. That extractor might have been faulty or just exceeded it's shear limits (sub-standard maybe). Buy quality parts and carry spare parts expecting to replace parts more often. The quickest fix is to take off that suppressor, but that of course defeats the whole point of getting it in the first place. My point is, if you are unwilling to fix the cause then you are stuck with mitigating the symptoms.

I'm thinking an AGB and heavier buffer/spring will take the edge off and this will work even better with careful choice of bullet and powder weight/type.

52' knows more about adjustable carriers than me so I'll be interested to hear how much this will help as well.

[LRRPF52]

What is a "cascading dead-blow" buffer? Is it like the endine, with the weights that move along a center post? Any any specific "extra power" buffer spring recommendations? I've never looked at them, but I assume there are various sorts and/or ratings, as with everything else in the "tune it yourself" world.

Thanks for the reply!

Cascading dead blow is when the buffer body in its forward momentum has the internal weights positioned to the rear until the bolt carrier slams into battery.

Once the carrier slams into battery, the buffer body no longer moves forward, but the internal weights that are still in motion continue forward and impact in a cascading sequence that is designed to counter carrier bounce off the barrel and extension.



The cascading internal weight dead blow effect is specific to the center-fired rifle cartridges in the AR15, mainly 5.56x45mm after the change from the early lots of extruded powder 5.56 cartridges from the early 1960s. When the Army switched solicitation to ball powder, it increased port pressure and cyclic rate, so one of the approaches to dealing with this was replacing the original spring guide to the buffer we know today as a rate reducer and cascading dead blow system to fight carrier bounce.

The Colt 9mm solid buffer with heavy weight is meant for the blowback-operated 9mm Colt SMG, which is an extremely violent little blaster if you've ever fired one. You should not use a 9mm SMG buffer in a rifle cartridge AR15.

If you feel you need additional buffer weight into the 4+ ounce region, I would look at spring weight first before buffer weight as a rate reducer on a suppressed set-up.

My 12" with Bootleg and Maxim kit using the tiny 2.9oz buffer is working great with the gas setting on fully suppressed.

Another thing I did was remove the O ring from the extractor.

The extractor O ring was a band-aid from the SOCOM suppressed M4A1 when they had no way to time the action, and were dealing with a lot of dwell time on the 14.5" M4A1 with KAC QD suppressor.

That combo increases cyclic rate and bolt torsional loads, causing...broken extractors and bolts, so they went to LMT who solved the problem with the LMT enhanced BCG.

The big Army prevented SOCOM from adopting it because they were afraid those BCGs would somehow end up in M16A2s and A4s, causing short-stroke malfs with the longer gas system and lower port pressure.

SOCOM then sought their own independent carbine with the SCAR program, settling on the ill-fated Mk.16, when they could have had a low-cost drop-in solution without skipping a beat.

[Klem]

52,

What are your thoughts on adjusting the gas at the block vs. at the carrier? You have a Bootleg carrier and I'm interested in how it's been and how better they are compared to other fixes like an AGB, buffer weight and spring strength, and combinations of the same.

Where does the gas vent?
How does the gun shoot and feel with this system?
I take it you don't need an AGB if you have an adjustable carrier?

Klem

[Mad Charlie]

Following this...

[tucansam]

LRRPF52,

You are an encyclopedia and my hero.

I have 9mm buffers in many of my builds. I will reconsider this approach.

Thanks.

[LRRPF52]

I'm a history buff of the AR15, among other things.

The technical aspects of the rifle, along with all the drama, military testing, back-and-forth between Army Ordnance, Gene Stoner, MacNamara's Whiz Kids, the USAF, early Vietnam experiences, all the way through the present is a very fun and engaging story.

A common theme from the technical side you will always see is how they approached balancing the timing of the cyclic rate, especially when changes are made to the system.

The AR15 was engineered originally around propellants like 8208M, which was clean and fast-burning, hitting the RLGS gas port with a very tame and consistent pressure, so that the rifle only needed a spring guide.

The original spring guides were known as the Edgewater Spring Guide, often referred to as a buffer in retrospect.

Edgewater Spring Guide on the Colt 601 and 602 rifles:


When the Army couldn't get consistent lot-to-lot powders based on the early extruded propellant that was used initially, they switched the powder solicitation to a common military ball powder, which was slower-burning.

That slower-burning powder created substantially higher gas port pressures, and took the rifle way out of timing with violent and early extraction. They did this without consulting Stoner or ArmaLite.

Along with tight chambers cut with ragged fortnight reamers, no chrome-lining in the chambers or bores, and no cleaning kits issued to Marines and Soldiers, some early Model 602 rifles started choking in actual firefights in Vietnam.

After many complaints and Marine officers who threw their careers away with letters to Congressmen, Congressional hearings were held on the matter with the Ichord Committee, where all of this bubbled to the surface.



One of the main changes was adopting a much heavier buffer that we all now know today as standard for the AR15, and it contained several weights with spacers in it to act as a rate reducer and counter to carrier bounce on auto.

Colt also introduced several different carbine AR15s in the early-mid 1960s, starting with the Colt 607 Commando, and later the XM177 and XM177E2 Commandos for mass production. These carbines got a shorter version of the rifle buffer, with a shorter spring and shorter RET. The 10" XM177 had problems maintaining consistent port pressure even with a moderator, so it was superseded by the 11.5" XM177E2 with more dwell time. Those guns run great and always have.

The 9mm Colt SMG is really an entirely different weapon only bearing resemblance based on the receiver shape, operating on blowback principle with no locking mechanism. It was a half-baked reaction from Colt in the 1980s after the Hk MP5 started dominating the LE market after the 1980 Iranian Embassy Siege in London, where Hk started getting orders from every department that could afford them around the world.





The mechanical engineering problems with the Colt 9mm SMG still haven't really been worked out, but I recommend against using its buffer when there are similar weight AR15 buffers with the internal weights available on the market. The trend in using Colt 9mm SMG buffers in 5.56 AR15s started with the machinegun collector's community where guys were building various length uppers with after-market parts, trying to tame down really short barrel and suppressed short barrel AR15s with varying degrees of success.

The best approach once you have a load and configuration dialed-in is to control the port diameter for the lowest temperatures the gun will see, then work outwards from there. We haven't had adjustable carriers for that long, so they are something that makes adjusting gas much easier than before.

As to the extractor:

One problem with extractors on suppressed guns is the torsional loading (rotational stress versus longitudinal/in-line stress) placed on the extractor, especially on a gun that is not timed and running a fast cyclic rate. As the carrier moves rearward too early and begins to cam the bolt out of a locked state, the case is still obturated to the chamber wall and doesn't want to budge.

The case head is firmly purchased to the bolt face and the extractor pocket ledge, with the extractor gripping the case rim. With excessive extractor spring force applied to the case, I don't think it helps extractor life, and I personally prefer a more relaxed extractor spring. This is why I removed my O ring and always remove O rings if I see them in a bolt before consider installing a bolt.

That O ring was a band-aid for the problems with the suppressed M4A1 with KAC QD can. I have yet to experience any extractions problems with any of the 6.5 Grendels I have built over the years.

[tucansam]

Put an adjustable gas block on the rifle and had it out today.

Adjusted the gas block to where the bolt no longer locked on an empty mag, then gave it 1/2 turn back open. Less felt recoil, and a lot less soot overall. Had the standard carbine spring and generic H2 buffer in, ran great. Put in an extra power spring I had picked up, no real perceivable difference, but I was once again worried about more stress on parts than was necessary, so I went back to the standard spring and called it a day.

Will shoot the rifle in this config for a few months and see what happens.

[VASCAR2]

Thanks for the update!