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Old October 3, 2021, 08:30 PM   #1
kymasabe
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AR cartridge stuck like Chuck.

Soooooo, I assembled an AR upper and having an issue I've never run into before. Cartridge loads ok, fires, and then the case gets stuck in the chamber and I have to beat it out with a dowel down the barrel. Also, extractor is ripping a piece of the case rim off. Barrel is a new old stock Bushmaster QRC barrel. I dont see any burrs in the chamber, its appears clean, but now thinking maybe there something in it like...cosmoline maybe?
I have no idea. Any ideas?
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Old October 3, 2021, 09:21 PM   #2
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I suggest you NEVER use a wooden dowel to drive anything out of a barrel.
I do not feel like writing the long explanation. Ignore my advice, you will be asking for help,and I will be cruel!!

I'm not hip enough to know what "QRC" is. Best to spell those out.

Stuck in the chamber with rim ripped off seems like action is opening vigorously while chamber pressure is still high. Brass has not relaxed.

What does that? Hmm. Well,you mentioned cosmoline. Care to elaborate? If there was preservative grease in the bore when you fired it.....Yeah,that could be it. We are supposed to clean preservative grease out then judiciously lube it.
Carbine? Rifle? Gas system? 5.56 or maybe 223? What ammo?

It helps if you fill in blanks.

It may be time to scrounge up a Sinclair bolt assembly tool and the bolt small parts. Your extractor had a bad experience, You'll need it some day.
Its a really good tool and the pins and springs go boing and whiz,neverto be found. Spares are good.
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Old October 3, 2021, 10:22 PM   #3
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Ok well, Bushmaster QRC barrel is from their Quick Response Carbine, is 16 inch, carbine length gas, not quite a pencil barrel but definately a narrow taper, with .625 gas block, no A2 front sight, no free float handguard, just a delta ring and standard handguard, chamber is 5.56 NATO with 1:8 twist barrel.
The stuck cases were both .223 and 5.56, both brassed cased.
There was preservative lube in the barrel and chamber when new, and I thought I got it all out with a brush and Hoppe's #9 and Gunscrubber, and did run a wet/lubed boresnake down the barrel when done. Now I'm wondering if I missed any excess preservative lube. I'll know more on Tuesday night when I tear it all apart. I have a spare/identical barrel I can try if there's something wrong with this one.
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Old October 3, 2021, 10:37 PM   #4
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All that ought to work. What is your ammo/load?
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Old October 3, 2021, 10:48 PM   #5
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I'd echo hibc's question. What ammo.

Sounds like you cleaned it fine

I have 2 guesses.
First is it a standard weight buffer and mil spec type bolt carrier? If badly tuned it could be opening and moving back too fast. But as violent as it's sounding I'm guessing not.

Second, it might be head space. Most people don't check it. Go-no go gauges are about $60 ish. Can cause over pressure issues.
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Old October 3, 2021, 11:15 PM   #6
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First round was a PMC bronze .223, 55gr fmj.
Second round was Lake City 5.56 green tip, I think that's 62 grain.
BCG is Toolcraft nitrided M16/full auto, whatever you want to call it bolt carrier.
Anderson buffer tube running Anderson spring and standard weight buffer.
I just put the same tube/spring/buffer and BCG in a 16 inch M4gery build, also carbine length, PSA barreled build, and it works great.
I don't have headspace gauges. I need to order some....right now.
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Old October 4, 2021, 12:26 AM   #7
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I bought a set after I built one and replaced a barrel on one. Both checked out. But it's a lot better to know for sure. Most parts are pretty good these days, but its still a possibility. In my experience pmc bronze is generally good ammo but not hot. It should run fine.
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Old October 4, 2021, 01:22 AM   #8
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extractor ripping through the case rim means the action is opening too soon. This is a gas issue. Opening too soon means too much gas is getting into the bolt carrier, too soon.

The direct impingement system used means that, in order to work right, the right amount of gas pressure has to arrive at the right time, so a balancing act between the gas pressure in the barrel (the ammo) the size of the gas port, the length of the tube and even the amount of spring tension holding the action shut are all factors.

the pressure curve of the ammo matters, it must be "in balance" with the rest of the factors, or you get the rip through the rim jam.

One test you can try is to remove the gas tube and test fire the rifle. If the case sticks then its probably something in barrel/chamber. If it works fine as a manually operated repeater, then the problem is the relationship of your gas system parts and the ammo pressure curve.

If your rifle's gas system is "out of time" then you have to figure out what part is the issue. One possibility is the barrel port size, but there are other possible causes as well. Consider an adjustable gas block, it should allow you to "tune" the gas supply to just "enough, on time".

Good Luck!
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Old October 4, 2021, 04:33 AM   #9
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Does sound like a possible combination of over-gassed and dwell time is causing your jam, before going "let's get radical" I would first drop the charged bolt on a cartridge and then extract it without firing to see if it gets stuck (obviously pointed at a safe direction with safety on) and also fire one cartridge which you hand-feed into the chamber. This would hopefully eliminate the possibilities of faulty chamber and perhaps point in other directions such as feed issues or aforementioned gas issues. My motto is "brass always tells the story" so look for other signs of possible over-pressure in the case (it would help to post pictures of them, the more details you provide the better your "internet gunsmith results" will be)
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Old October 4, 2021, 07:14 AM   #10
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As both Bushmaster and Remington are now defunct,its hard to say what specs those barrels were made to.
Perhaps they were being held in the "non-conforming parts" cage.

I cannot tell you what your gas port size is or what it should be.

As you had the problem with two different types of factory ammo,I doubt ammo is your problem.

As your barrel is marked 5.56 and you have a 1 in 8 twist, the 223 chamber question is answered. No problem.

You might be able to make some progress by going to a heavier buffer. They are marked with No Mark, or H-1 , H-2, etc. It wont hurt to try.

But as 44AMP suggested,the most straight line cure for your problem (if its over gassed) is an adjustable gas block. I don't know which to recommend.

From what you described,I do not think your original gas block is attached via tapered cross pins. Thats a good thing. Seems like a straight forward gas block R+R is the straightest line between two points. Probably!
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Old October 4, 2021, 07:26 AM   #11
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The most common cause of this anomaly in an AR is nothing more than a rough chamber in which the case can stick to varying degrees. Your brass should tell the story. If so, a simple smoothing (less than 5 minutes) of the chamber will remedy the issue.
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Old October 4, 2021, 08:18 AM   #12
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Originally Posted by imashooter View Post
The most common cause of this anomaly in an AR is nothing more than a rough chamber in which the case can stick to varying degrees. Your brass should tell the story. If so, a simple smoothing (less than 5 minutes) of the chamber will remedy the issue.
If that's the case, how does one go about smoothing/polishing the chamber? Dremel with a felt polishing bit and a little jewelers paste? 1000 grit sandpaper?
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Old October 4, 2021, 08:48 AM   #13
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It may indeed be a chamber surface finish issue .

I used to build and finish plastic injection molds. Surface finish is a big deal with the "extraction and ejection" cycle of a running mold.

I understudied a Master Mold Finisher and learned some things. The polishing grit,regardless what form of abrasive you use, cuts its own texture of grooves.

In the mold biz,we think in terms of "direction of draw" Its the same as "Direction of extraction" in a gun.
When the stoning or polishing lines of texture from the abrasive are perpendicular to the direction of draw,they act like threads. They are "tooth" that locks the cartridge brass in he chamber. Finer grit makes for finer "threads" but still,they work against you.
Now ponder what you get using a lathe or Dremel or drill going roundy round in your chamber. Micro-threads.

We polish molds stroking in the direction of draw. Movng inny-outy in the chamber,rather than roundy roundy..

Also,polishing,less is more. You won't fix a butchered chamber. This is not about removing reamer chip rings in the chamber.

It about knocking the high spots...the tips of the microscopic "hair" of the finish off. Just put plateaus on the peaks . Don't worry about the valleys.

I did a lot of work with cast iron or brass laps and diamond abrasive compound.
Brass is really good at allowing grit to embed in the brass. It then holds the grit as a cutting tooth,and becomes like a file.

HMMM. We have cartridge brass that conforms to the size and shape of the chamber,pretty much.

So if we were to embed a very fine polishing grit in our cartridge brass,and carefully stroke it in and out of our chamber, we might polish the chamber in the ideal direction.

I can think of two methods. One is drill and tap the primer pocket ,thread in a rod,and use it for a handle to manually stroke the brass as a lap.

The other way would be to embed the abrasive into loaded rounds (perhaps mild reloads) and simply fire them. It would fit the chamber perfectly and cut down the peaks of the "teeth" in the surface finish.

Now, I have years of professional experience polishing molds. I can't teach you everything in this post,

I'd use Gesswein green # 9 diamond compound. I might get it from Gesswein, MSC,or DME. It is a grit and grease compound,about like avocado Crisco. It comes in a hypo syringe. I suggest the small one..
I.d apply a sparing amount to the body of the brass then burnish it in a bit with a hard dowel pin...just to be sure a good amount of grit embeds.

I might leave a minimal trace of the diamond compound,just a trace film,on the body of the case. As little as possible. None on the neck and shoulder.

I think I'd do about 10 , then clean up the gun and see how it does. It might take 10 more, That should make the difference.

Or,use the same diamond compound manually with a drilled and tapped cartridge brass. Work a portion of the chamber about 10 minutes on the clock face wide.(This is about a portion of the chamber to work. It has nothing to do with time.) use about a 1/4 in stroke. Keep the brass full flat contact in the chamber, Dont rock it. You don't want to bell the chamber. Work that segment,then rotate the barrel a bit,and work another segment about 10 minutes of the clock face. You can use a little mineral spirits for lube.
I'd guess 30 seconds or so per segment. Probably not over a minute ,

Then clean it up good. Get all the grit out and shoot it.

Thats how I would do it.

Last edited by HiBC; October 4, 2021 at 08:58 AM.
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Old October 4, 2021, 09:00 AM   #14
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It may indeed be a chamber surface finish issue .

We polish molds stroking in the direction of draw. Movng inny-outy in the chamber,rather than roundy roundy..
Had me laughing out loud, but makes perfect sense !! THANK YOU !!
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Old October 4, 2021, 12:14 PM   #15
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Quote:
Originally Posted by HiBC View Post
It may indeed be a chamber surface finish issue .

I used to build and finish plastic injection molds. Surface finish is a big deal with the "extraction and ejection" cycle of a running mold.

I understudied a Master Mold Finisher and learned some things. The polishing grit,regardless what form of abrasive you use, cuts its own texture of grooves.

In the mold biz,we think in terms of "direction of draw" Its the same as "Direction of extraction" in a gun.
When the stoning or polishing lines of texture from the abrasive are perpendicular to the direction of draw,they act like threads. They are "tooth" that locks the cartridge brass in he chamber. Finer grit makes for finer "threads" but still,they work against you.
Now ponder what you get using a lathe or Dremel or drill going roundy round in your chamber. Micro-threads.

We polish molds stroking in the direction of draw. Movng inny-outy in the chamber,rather than roundy roundy..

Also,polishing,less is more. You won't fix a butchered chamber. This is not about removing reamer chip rings in the chamber.

It about knocking the high spots...the tips of the microscopic "hair" of the finish off. Just put plateaus on the peaks . Don't worry about the valleys.

I did a lot of work with cast iron or brass laps and diamond abrasive compound.
Brass is really good at allowing grit to embed in the brass. It then holds the grit as a cutting tooth,and becomes like a file.

HMMM. We have cartridge brass that conforms to the size and shape of the chamber,pretty much.

So if we were to embed a very fine polishing grit in our cartridge brass,and carefully stroke it in and out of our chamber, we might polish the chamber in the ideal direction.

I can think of two methods. One is drill and tap the primer pocket ,thread in a rod,and use it for a handle to manually stroke the brass as a lap.

The other way would be to embed the abrasive into loaded rounds (perhaps mild reloads) and simply fire them. It would fit the chamber perfectly and cut down the peaks of the "teeth" in the surface finish.

Now, I have years of professional experience polishing molds. I can't teach you everything in this post,

I'd use Gesswein green # 9 diamond compound. I might get it from Gesswein, MSC,or DME. It is a grit and grease compound,about like avocado Crisco. It comes in a hypo syringe. I suggest the small one..
I.d apply a sparing amount to the body of the brass then burnish it in a bit with a hard dowel pin...just to be sure a good amount of grit embeds.

I might leave a minimal trace of the diamond compound,just a trace film,on the body of the case. As little as possible. None on the neck and shoulder.

I think I'd do about 10 , then clean up the gun and see how it does. It might take 10 more, That should make the difference.

Or,use the same diamond compound manually with a drilled and tapped cartridge brass. Work a portion of the chamber about 10 minutes on the clock face wide.(This is about a portion of the chamber to work. It has nothing to do with time.) use about a 1/4 in stroke. Keep the brass full flat contact in the chamber, Dont rock it. You don't want to bell the chamber. Work that segment,then rotate the barrel a bit,and work another segment about 10 minutes of the clock face. You can use a little mineral spirits for lube.
I'd guess 30 seconds or so per segment. Probably not over a minute ,

Then clean it up good. Get all the grit out and shoot it.

Thats how I would do it.
Great post.
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Old October 5, 2021, 11:19 AM   #16
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Quote:
If that's the case, how does one go about smoothing/polishing the chamber? Dremel with a felt polishing bit and a little jewelers paste? 1000 grit sandpaper?
Quick / ez method is to use a cleaning rod chucked in a drill. For a .223/5.56 I use a .38 mop attachment with some Flitz. I normally do approx 6-8 sessions of around 60 seconds at a moderate speed. Normally apply more flitz a few times. As you drill, slowly move the rod in and out a bit. Not out much or you'll be slinging flitz all over. Even a decent abrasive toothpaste like colgate, etc will work. As does pearl drops. Probably a wheel polish too. Never seen a need to polish. I only give them a decent smoothing as needed.
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Old October 5, 2021, 01:59 PM   #17
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I love you guys, but here is what happened:
A fella has brass stuck.
44Amp advises to check the headspace, next remove the gas tube. This troubleshoots the problem to overpressure, gas system timing, or chamber roughness.
Everyone jumps on board with their favorite technique for polishing the chamber. Even though it might be fine and we have no report of what the pounded out brass looks like.

Someone should offer to loan the fellow some chamber gauges. Sell them to him and buy them back when he returns them. Then we’ll know that measurement is in spec.

Then pop the gas tube out, and fire a shot with known good ammo. It could be ammo, so try a new box of white box. The case will jam or not. If no jam, it could be the old ammo is bad or the timing is bad.

Hook up the gas tube. Fire a shot. If it doesn’t jam, it’s an ammo problem.

Polishing the chamber won’t hurt but we don’t know if the chamber is rough.
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Old October 5, 2021, 07:45 PM   #18
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No.
Quote:
The most common cause of this anomaly in an AR is nothing more than a rough chamber in which the case can stick to varying degrees. Your brass should tell the story. If so, a simple smoothing (less than 5 minutes) of the chamber will remedy the issue.
No.
Quote:
Quick / ez method is to use a cleaning rod chucked in a drill. For a .223/5.56 I use a .38 mop attachment with some Flitz. I normally do approx 6-8 sessions of around 60 seconds at a moderate speed. Normally apply more flitz a few times. As you drill, slowly move the rod in and out a bit. Not out much or you'll be slinging flitz all over. Even a decent abrasive toothpaste like colgate, etc will work. As does pearl drops. Probably a wheel polish too. Never seen a need to polish. I only give them a decent smoothing as needed.
No.

ARs ripping chunks out of the rim do not indicate a rough chamber. It indicates being over-gassed.
The gas system is getting too much pressure and the bolt is opening too soon / too violently.

Polishing the chamber is a bandaid treating a symptom, not a cure for the disease.

More than likely, the gas port is too large.
Were these barrels originally intended for an adjustable gas block?
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Old October 5, 2021, 07:53 PM   #19
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OK,Stinkyete. Have fun feeling superior.

The OP had his problem with two different varieties of factory ammo..

Its highly unlikely two different factory loads would be overpressure.

So much for it being an ammo problem.(at least its unlikely)

Ip to this point,most of the dialogue was about getting critical info from the OP.

While I do practice checking headspace on every build I do, IMO the symptoms do not point particuarly at headspace. I'll give it a maybe,but unlikely.

44AMP offered a rational assessment.Among the most likely is being overgassed.I'd give that about 8 out of 10.
And I'll say again, IMO,an adjustable as block is the straightest line between two points to cure the problem. Probably.

But its also true that a NOS Bushmaster barrel might have been left over because it was quarantined in the QC process,

Two possible spec problems are gassing (we covered) and chamber surface finish,as suggested by Kymosabe. That thought has merit.
I have seen extraction problems due to factory chamber finish issues.

One of the WORST things about TFL is the people lurking in he wings who never offer an original positive thought,never have anything useful to offer.

They look at other folks posts as clay pigeons at the sporting clays range.

If I wrote what I thought about those folks,the Moderators would be unhappy.

The OP asked for advice on how to go about improving his chamber.

I knew it was inevitable well meaning people would offer bad advice.

Bore brushes,mops,tampons and other objects have no shape definition.

Form and dimension are critical to a chamber. Yarn,rags,felt,brushes,etc wallow material off with no regard for form or dimension..

Spinning something with filaments in the chamber ,such as a bore mop, will cut material off the peaks of the surface texture, but it also reaches down into the valleys and cuts them deeper at the same time.

And spinning something in the chamber "roundy round" is easy, but the lines of cut are the WRONG DIRECTION. They are like fine threads.

As I said,my employer bought plane tickets and a room at the Marriot for a week so I could understudy a Master mold and die finisher. When I arrived,he was polishing coining dies for the US Mint.

I don't know if you have any idea what is involved with polishing mold surfaces to hit blueprint designated tolerances for flatness,form, dimension and RMS, but I got paid good money to do just that.

A good example of what can be done wih "fluff and buff" is to look down the barrels of a reblued shotgun. Look at the highlghts. The distortion,waves.

The standard I had to work to (sometimes) was it had to look like an optically correct mirror.

There are satellites in the sky that use light beams for controls. They have hand polished tungsten carbide mirrors to direct those light beams. The total tolerance for flatness across those mirrors is .0001 inch. How do I know that? The satellite company told my boss the mirrors I polished were the best they ever got.

And funny thing,I've chambered a number of rifles. Even made my own reamer once.

The secret of a good polish is a good tool finish. The precision is in the reamer. The less you do to ruin the reamers work,the better.

Yes,sometimes there is a little microscopic "hair" Yes,some may be gained by turning the peaks into plateaus. Go back into a chamber with a reamer that has a chip across a flute and you gouge a ring there is no hope of polishing out...though some will try.They may actually sand out enough steel to pass it off,but now the chamber is oversize,and probably belled or jugged.
The sandpaper wound around the stick washed out the precision the KO Lee or Browne and Sharpe cutter grinder put in the reamer.

But lets say you have a peak to valley depth of .001. If you take .00025 off the peak,you have created surface area for the mating part to rest on.

So long as you can still see the valleys,you know you have taken less than .001. And if your original finish,such as a grind or EDM finish,truly was .001 deep,you know you held to less than .001 dimensionally.

By taking .00025 X2.both sides of the chamber, the chamber got 1/2 thousandth bigger.

I work stroking in and out,about a 10 minute zone on the clock face using brass that conforms to the geometry of the chamber. I can use my loupe or endoscope to see the texture change evenly. Then I can do another zone.

Many times in the business I was in my work was checked with profilometers and dial indicators.

I did not contradict imashooter. I just gave the OP the best I could ,practical to what he could easily do.

The OP can make up his own mind. But THE OP ASKED HOW. I answered.

And my best answer to his original problem was an adjustable gas block,which I suggested before even mentioning polish.

I do not,as a rule,advocate people doing any amateur work to a chamber or bore. Or a sear.

Our OP began by talking about beating on a wooden dowel.

But if he was bent on the idea of chamber polishing, I wanted to offer him better guidance than clover valve grinding comound on a tampon driven by an unlicensed Dremel Or sandpaper on a stick.

Last edited by HiBC; October 5, 2021 at 08:09 PM.
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Old October 5, 2021, 08:38 PM   #20
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To answer someone's question...the gas block is pinned in place with tapered pins. Think of an A2 front sight that pinned in place, with the sight sawed off and only the gas block remaining. That's what it looks like.
And, my understanding of why there are surplus barrels is...when bushmaster closed, the excess barrels were sold to places like CDNN who stacked them deep and sold them cheap. I have two of these things and I'm very close to chucking them both and buying another barrel, but I can't find a pencil or tapered barrel like a faxom gunner in carbine length gas, they're all mids.
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Old October 5, 2021, 08:57 PM   #21
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OK,well,with that info,the adjustable gas block idea could probably be done but I don't like the tranverse slots that accomodated the taperpins.
I think I saw adj gas blocks in a Midway ad today for $90.
Could be good money after bad.
I'm not sure what they have in stock today,but try Aero Precision for a barrel.

For my money, would the mid gas system be so bad?

Last edited by HiBC; October 6, 2021 at 07:40 AM.
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Old October 5, 2021, 11:00 PM   #22
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Well, we're trying to keep the rifle light. Mid length moves the gas block and a little weight a little farther forward. I'd still want to mount a handguard cap behind the gasblock and use a polymer handguard like a Magpul or B5, and a delta ring. But, can I use a handguard cap with a gas block that installs with set screws? I usually dimple my barrels with a Kaw Valley jig so I get perfect gas port alignment, and I usually bury it under a free float handguard. I can't remember if there's ever a gap between the gas block and the shoulder on the barrel to accommodate a handguard cap.
If there's a gap, I'd consider going that route.
Option #2: couldn't I just send my existing barrel to a pro to have the chamber measured, reamed, cleaned up?
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Old October 6, 2021, 07:14 AM   #23
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Quote:
Originally Posted by FrankenMauser View Post
No.

No.

No.

ARs ripping chunks out of the rim do not indicate a rough chamber. It indicates being over-gassed.
The gas system is getting too much pressure and the bolt is opening too soon / too violently.

Polishing the chamber is a bandaid treating a symptom, not a cure for the disease.

More than likely, the gas port is too large.
Were these barrels originally intended for an adjustable gas block?
Quote:
No.
Quote:
The most common cause of this anomaly in an AR is nothing more than a rough chamber in which the case can stick to varying degrees. Your brass should tell the story. If so, a simple smoothing (less than 5 minutes) of the chamber will remedy the issue.
No.
Quote:
Quick / ez method is to use a cleaning rod chucked in a drill. For a .223/5.56 I use a .38 mop attachment with some Flitz. I normally do approx 6-8 sessions of around 60 seconds at a moderate speed. Normally apply more flitz a few times. As you drill, slowly move the rod in and out a bit. Not out much or you'll be slinging flitz all over. Even a decent abrasive toothpaste like colgate, etc will work. As does pearl drops. Probably a wheel polish too. Never seen a need to polish. I only give them a decent smoothing as needed.
No.

ARs ripping chunks out of the rim do not indicate a rough chamber. It indicates being over-gassed.
The gas system is getting too much pressure and the bolt is opening too soon / too violently.

Polishing the chamber is a bandaid treating a symptom, not a cure for the disease.

More than likely, the gas port is too large.
Were these barrels originally intended for an adjustable gas block?
"extractor is ripping a piece of the case rim off........" CHUNKS? A bit of dramatic BS; No?

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Old October 6, 2021, 11:38 AM   #24
FrankenMauser
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Very helpful reply.

Quote:
But, can I use a handguard cap with a gas block that installs with set screws?
Yes, as long as the gas block and/or barrel are dimensioned for it (most are), and won't block the gas port (though the effect of that is debatable, too).
I've done it on two builds. You just need enough room to squeeze a cap between the gas block and the shoulder on the barrel.
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Old October 6, 2021, 04:29 PM   #25
BornFighting88
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Could it also be his recoil assembly?? I get that it is over gassed, that makes complete sense to me. It is opening too soon, chamber pressure too high and brass hasn’t relaxed yet. This would allow the extractor to rip off that thin small rim. I buy that.

There are some that believe the standard Mil-Spec recoil buffer assembly is for rifle length gas systems. I don’t necessarily follow that path. Gun designers (usually) aren’t dummies, and they make working products. But in this case, I would pose that question, just to say I did. Could a more stout or heavier recoil buffer help?? If the system has to move more weight/mass before it can start its cycle, could it be opined that a heavier buffer could aid in (not completely solve) this situation??
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