Extractor - Out of Spec or Tolerance stacking ....

[StoneHendge]

Without going into too much detail, I relaced the extractor on my JP bolt as a precautionary measure with one from Black Rifle Arms back in the Fall. At the same time, I also ordered a spare bolt from BRA. I began to have feeding problems off of a full mag in my 6 ARC and thought "here we go again". I replaced the extractor spring, tried it with and without the insert or donut and couldn't get it to work properly. The bolt would stop short of the final push needed to get the extractor over the rim. If I wasn't feeding off of a full mag, it would usually work, but often it didn't. At which point I decided to sideline it. I put my 22" JP 6.5G with 5k+ rounds in the rifle that was for my defective and unwarranted Lilja AR24 6 arc barrel and figured I would give it a try in Open in a Quantified Performance match back in November. It practiced well on the Thursday before the match - until I decided to make sure that it would feed off of a full mag. Which it wouldn't. I tried trouble shooting it with both bolts and dummy rounds at home, but ended up bailing on the match since I didn't have 160 rounds of match ammo made for another rifle that would actually be reliable.

At this point, I've entered the "Eff the .445 case head" zone. I pulled the Grendel barrel and bought a 20" JP .223 and have spent time focusing on that and other things

I finally mustered up enough mental energy to get back to the arc and ordered a Maxim bolt since my 16" Lilja arc is headspaced to them. It took 2 weeks for Maxim to actually get around to shipping it and then 8 days for the USPS to get it 150 miles as the crow flies. It was worth the wait, I guess, since it actually works!

At which point I start kicking myself in the arse for not realizing that the extractors from the same vendor were the problem all along. The Maxim extractor is 0.065" when measured from each side of the lug on the extractor to the bottom of the lip. Both of the BRA's measure 0.08". I have the extractor I pulled from the JP bolt somewhere, but I can't currently find it to measure it. But its pretty easy to see the problem here with the wear on the tops of the extractors (BRA bolt on left, JP on right):

BRA Extractors.jpg

The longer lip has been pushing the extractor up too far and it either can't clear the barrel extension, or the friction is causing too much lost momentum.

So the question is, are these extractors flat out out of spec? Are they the wrong extractors (perhaps for a 6.8 bolt)? Or is it perhaps a result of tolerance stacking with the extractor being a little big and perhaps the barrel extensions being a little tight.

[montana]

I hate the word tolerance stacking. Parts are either in spec (tolerance) or they're not. They do not stack. Parts have a +- tolerance and if both parts are in those tolerances they will work.

Two parts can have an interface tolerance. Two parts can be out of spec and work quite well if the interface tolerance between the two parts is in tolerance. Make sense?
I have no TDP sheet for the 6.5 Grendel extractor. Best method is what you are doing, comparing the good extractor that works and the bad ones that don't. Some times the extractor pivot pin location will be off, causing lift, feed and chamber issues.

[LRRPF52]

Guys, at this point, you really should be using the Rexus Ultrabolts and don’t look back.

There are dimensional changes to the lug roots and bolt head to increase strength in critical areas, and the extractors work.

I personally pull any O ring I find in a bolt, including from 5.56 guns, because the O-ring was a band-aid for early SOCOM profile M4A1 barrels that had tight chambers. Those guns had extraction problems, so Crane added the silly O-Ring to deal with it. Real solution was running correct reamers and adhering to Mil-Std specs, and going with a field-usable adjustable gas system to select between suppressed and unsuppressed with the high back pressure KAC NT4 can.

Anyway, if you keep the O-Ring in the extractor, the amount of force required to snap over the case rim is higher, and also puts more stress on the extractor lip as it’s going into battery.

Another factor in positive bolt lock-up from full mags is an extra power action spring.

But yeah, I would never fault someone for going with a gun that actually goes bang for a match, than one that doesn’t.

[StoneHendge]

I'd be hard pressed to think that a Rexus Ultrabolt would work in these barrels. I read "Restores claw geometry to 100% mil-spec 5.56 strength" to mean that they are larger. 5.56 bolts are around 0.09" measuring like I did above, so there is absolutely no way one would clear the barrel extensions with the wear I'm getting with an 0.08" extractor. They may clear other barrel extensions - but I doubt they'd clear mine.

Yeah, I took at the O-rings and tried it with spring / insert only. I took out the inserts and tried it with spring / O rings only. None of that worked so I ordered Sprinco kit and tried all the possible combinations and none of that worked.

I'm beginning to think that perhaps the Lilja and JP barrel extensions are on the tight side of "spec" where the bolt clears the lugs in the extension. I use quotes because "spec" frankly seems to be a rather loosely used term.

JP includes their bolts with a barrel and tells you that you're on your own if you decide to use someone else's bolt or bolt parts. I choked when I saw that a JP extractor is over $60. But the amount of time I wasted trying to troubleshoot was worth a heck of a lot more than the $40 I saved going elsewhere.

Lilja recommends Maxim bolts and the Maxim bolt that I originally used with the barrel worked very well. Unfortunately, the extractor broke after about 1k rounds. I'm thinking that maybe that's because the lip is on the short side and I see no reason expect the new one to last any longer.

I'm pretty much at the point where I'll only buy JP or Proof barrels moving forward (Proof recommends using JP bolts) and just suck it up and pay for JP extractors knowing that it's saving me sanity down the line.

[LRRPF52]

ETA: Barrel extension problem intruding on the extractor snap-over range of motion, grinding the extractor. I didn’t look at the zoomed-in photos.

Trust me. Get the Ultrabolt.

Everyone is using standard AR-15 barrel extensions, so Ultrabolt works like any other in terms of mechanical interface.

They are just stronger.

I just looked over some bolts from one of the top tier manufacturers for 6mm ARC, and they didn’t add any of the dimensional strengthening features.

ARC is a bit harder on the bolt due to smaller bore volume, higher pressures elongated over barrel time, and run at slightly higher chamber pressure.

Ultrabolts are Vacuum Arc Remelted to get rid of the sulphur. Sulphur is great for machining, but not good for strength.

Ultrabolts also have much thicker bolt head walls, and thicker bolt head support.

There are strengthening radii on the back-end of the bolt lugs, and inside of the bolt face and inner bolt walls.

Ultrabolt is the easy button.

[StoneHendge]

Trust me. Get the Ultrabolt.

Everyone is using standard AR-15 barrel extensions, so Ultrabolt works like any other in terms of mechanical interface.
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Can you measure the depth of the ultrabolt extractor claw like I outlined above? If it's near .08" or greater, then it will not work in my Lilja barrel. And if whatever that is is considered "in spec", then my barrel extension should be considered "out of spec". Which would answer my question and the reason for the thread.

[LRRPF52]

Can you measure the depth of the ultrabolt extractor claw like I outlined above? If it's near .08" or greater, then it will not work in my Lilja barrel. And if whatever that is is considered "in spec", then my barrel extension should be considered "out of spec". Which would answer my question and the reason for the thread.

I didn’t zoom in on your original photos. Had I done so, I could have seen what the problem is straight away.

Your extractor outer lip surfaces are being ground by the ID of the barrel extension teeth during snap-over.

This is caused by extensions that are heat-treated after feed ramps have been ground.

The part is no longer symmetrical, so the heat loading affects the area with less mass (feed lips) and the part goes slightly oblong or egg-shaped.

Bill told me about it when he was doing initial development of the system, so it has to be accounted for in processes by the extension manufacturer.

It wouldn’t matter with a 5.56 or any cartridge with a .378” case head because the tolerances are generous.

I did go and measure 2 bolts quickly.

Maxim bolt extractor ordered back in 2014 I think: .070”
Rexus Ultrabolt extractor: .084”

I double-checked some of my more used-and-abused Grendels, and don’t see any of this grinding. It’s something I do look for any time I’m doing post-range inspections and cleaning, though I admit that I am not anywhere near as attentive with cleaning these days.

Several ways you can go with this:

Return
Apply your Holiday Inn Dremology skills to relieve the ID of the offending extension lugs.

[LRRPF52]

I just checked my Lilja 17.6” and Larue 18” guns as well.

No grinding marks at all on the extractors in those surfaces adjacent to the reinforcement spine/lug.

For any manufacturer who is spec’ing barrel extensions for 6.5 Grendel, 6mm ARC, 22 ARC, 338 ARC, etc., you need to inform the extension vendors that the ID of the finished part needs to be held to a very high standard of dimensional uniformity.

Right now, the industry is suffering across all sections of the manufacturing chain as skills gaps permeate the work force and young managerial class, who didn’t respect the knowledge and experience of the older managerial and entrepreneurial class that laid the foundations for specifications, processes, and procedures.

So we’re seeing things de-tune a bit, even among the most respected brand names in the industry, with few exceptions.

I am inspired by some of the up-and-comers though. I recently had an experience touring a manufacturing facility that is holding itself to standards that nobody else would even consider because of the costs and technical expertise required to maintain their standards.

[StoneHendge]

Thanks 52. Yeah, I was going to try and blow up the pictures last night but it was getting late. The full bolt on the left and the extractor on the JP bolt on the right both have no more than 100 rounds fired on them, and then probably a like amount of attempts to strip and lock down a dummy cartridge, I'm glad to hear/realize that the problem wasn't with Black Rifle Arms since I've generally found them to be a good inexpensive vendor.

Since the barrel has 3500 rounds on it and goes back to 2020, I don't have the mental fortitude to even think about dealing with Carson after my AR24 loose barrel extension. And I do not trust my Dremel skills. I'll probably either see if Maxim will sell me an extractor ala cart or just get another bolt from them as a back up. Hopefully that gets me to the point where the barrel is shot out and I can move on. I'm certainly not expecting much in the way of life from the smaller extractors in a 16" middie.

Right now, the industry is suffering across all sections of the manufacturing chain as skills gaps permeate the work force and young managerial class, who didn’t respect the knowledge and experience of the older managerial and entrepreneurial class that laid the foundations for specifications, processes, and procedures.

Unfortunately, it's becoming apparent that this problem isn't limited to the firearms industry.

[BluntForceTrauma]

I'd be hard pressed to think that a Rexus Ultrabolt would work in these barrels.

Hate to say it, but I kinda agree with SH here. Our Rexus UltraBolt is strengthened to the point of slicing the clearances very thin, and if an existing extractor barely clears the tight inner diameter of his extension, ours wouldn't do any better.

[StoneHendge]

Hate to say it, but I kinda agree with SH here. Our Rexus UltraBolt is strengthened to the point of slicing the clearances very thin, and if an existing extractor barely clears the tight inner diameter of his extension, ours wouldn't do any better.

Is there a published spec on the size of the extractor - either the way I measured it or some other way? I feel compelled to let Lilja know how much time, money and agony (including going down at matches) this barrel has cost me.

[LRRPF52]

Bill set up a sheet of specs for 6.5 Grendel AR-15 unique components, and the barrel extension concentricity post-heat treat was one of them.

You can get away with eccentric extensions in 5.56, but not with .441” case heads, as you found out.