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Old April 27, 2010, 12:29 PM   #1
CowTowner
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A short while ago, I built an AR type rifle in 7.62x39mm caliber.
Once assembled, the bolt did not travel all the way to the rear when fired.
I tried PMC, Privi Partizan and Wolf ammo without any change.
The next round in the mag would not feed. The last round would not lock the bolt open.
I contacted the upper supplier and was advised to send the upper and bolt carrier to them for repair. After getting it back I inquired as to the cause of the failure and was told the issue was "The carrier was fouled and the gas rings were misaligned.".
Now I'm not the brightest bulb in the pack, but I still remember how to clean and assemble the bolt carrier group on an AR type rifle. I learned in the 70's when issued an M-16A1 in the Army.
I understand what "the gas rings were misaligned" means. I'm not sure I agree with that, because I know I checked them more than twice.

So, what exactly does "The carrier was fouled" mean?

Oh yes, I was warned that available ammo was under powered and may not cycle the action correctly as well.
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Old April 27, 2010, 01:29 PM   #2
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So, what exactly does "The carrier was fouled" mean?
It means it needed to be cleaned. It may just be tech-talk for "we don't know" or "we won't tell", or the bolt carrier may have been heavily fouled by the ammo you were firing.

I don't buy the gas ring misalignment explanation, I have seen ARs fired without gas rings and they worked fine, the gas rings are just a little bit better seal as the BCG gets worn or dirty.

BTW, 7.62X39 operates at lower pressure than 223/5.56 NATO, so that may really be critical on a DI design. Who knows?
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Old April 27, 2010, 01:31 PM   #3
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He is telling you that the fouling on the carrier was hot gas fouling. In the field I always kept a bottle of duck snot, (LSA), in my pocket and ran my gun wet. I didn't have that problem but couldn't convince most people to do the same. You need to get anal about cleaning your gun after shooting and not let the fouling sit there and get hard. That being said most people don't have that problem unless they are in dirty conditions or are firing a lot. I mean a whole lot, buckets of lot.

I have an ammo can specifically for that on my bench, the parts get dumped in the can and its filled with fuel oil, a little ATF, a little WD-40, a little gun oil, there is no specific formula. Mostly its just fuel oil and ATF. I understand some people use brake fluid, I haven't tried it but whatever works.

When I get around to it all I have to do is wipe or brush off what crud is still there, blow it dry with the compressor and reinstall. No need to lube it at that time. When the oil gets dirty I just filter it and replace whats missing. I change it out about every 10 years whether I need to or not.
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Old April 27, 2010, 02:09 PM   #4
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OK, I can buy hot gas fouling if lots of ammo is fired.
I managed to single shot less than 100 rounds through the gun before it was sent back.
Oh yea, I disassembled the bolt carrier group and cleaned it before I sent it. Also brushed the chamber and barrel and put some light oil in it as well.
Well, I'll load some hand loads for the next test and see what we will see.

Thanks for the responses and I'll be looking for others as well.
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Old April 27, 2010, 05:51 PM   #5
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I would be inclined to feel that if they fixed the problem I wouldn't care what they said was wrong.

Jim
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Old April 28, 2010, 08:36 AM   #6
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I would be inclined to feel that if they fixed the problem I wouldn't care what they said was wrong.
Jim, I'm just not built that way.
We'll see if it's fixed when I get to the range this weekend.
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Old April 28, 2010, 12:10 PM   #7
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CowTowner-
Since it sounds like there was little or nothing wrong with the upper assembly, I would look carefully at the lower. If it were me, I would make sure the gas key is tight and the buffer spring assembly comes out of the rifle, gets cleaned, and gets lubed well before going back into the rifle. Then, when you take your range trip, either the problem will have been fixed, or you will have eliminated another possible source of stoppages.
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Old April 28, 2010, 01:27 PM   #8
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Scorch,
Thanks for the tips. I have already prepped the buffer and spring with a cleaning and light oiling. I also made sure the Timney trigger group was mounted properly and oiled. The gas key on the top of the bolt carrier is tight and peened into place.
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Old April 28, 2010, 07:29 PM   #9
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I'm with the others on the rings and gas key. I worked on thousands of M-16s and that is what the book answer is. It almost never is the answer. I talked with a guy a while back that bought a new .223 with the same problem. Under warranty and he sent it back. They gave him the same line after repairing it and had installed a new key. It did not function properly. Back it went. We knew what was wrong but he had the warranty yet. It came back right the second time with a note saying they reamed the gas port. If you use the old style F/sight assy., with the tapered pins, chances are the gas bleeder hole is out of alignment enough to choke the gas
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Old April 29, 2010, 10:00 AM   #10
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I have a low profile gas block installed, but I can sure take a look at the port if it fails after testing this weekend. Thanks for the pointer. It has been added to my list.
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Old April 29, 2010, 10:30 AM   #11
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If the AR is short stroking, check your buffer and spring. If the spring rate is too high or the buffer too heavy you will have cycling problems.

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Old April 29, 2010, 11:14 AM   #12
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Joat, If you're aware of a different buffer spring for the 7.62x39mm version, I'd be happy to know about it. All I have ever found is a standard and a short (M4).
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Old April 29, 2010, 02:22 PM   #13
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From experience:

If your shooting inside 300 yards you can shoot the rifle till your blue in the face with gas rings misaligned and you'll NEVER see it on paper.

At 600-beyond its a different story.


I spent three years in Iraq as a security contractor. My last year and a half was as the chief range officer for the Baghdad Embassy Security Force. I put over 60K rounds (three upper receivers worth) of ammunition through my M-4 during that time. I rarely cleaned it. RARELY means maybe (stress maybe) I wiped the bolt with an oily rag now and then.

I did however religiously lube the **** out of the thing with good ol CLP.

A direct gas operating system needs to run wet. Sloppy wet. If it does it'll be a rare event that it effs up. Dry it out cause you don't like slimy hands and you'll soon become proficient at immediate action drills to clear the stoppages/malfunctions.

Good luck.

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Old April 29, 2010, 07:05 PM   #14
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None specifically. When we are diagnosing a "problem" AR we go to the "tub o springs" and find one that lets the gun cycle. The tub contains a mix of buffer springs most from Wolff. If that doesn't fix the problem we tailor the buffer weight + or - until it does.

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Old May 3, 2010, 07:52 AM   #15
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Well, here's the range report after the disclaimer....
I took the bolt carrier group apart and sprayed it down with CLP Saturday and let is soak. The bolt itself was the one I sent back. The carrier? Well I'm not in a position to swear it was the same one. Anyway, I reassembled the critter and then put the rifle back together.
Took it to the range and it cycled as it should have all along.
It ate Privi and Remington ammo without issue.
The issue is resolved.
LongRifles- When I was in uniform in the late 70's, we fired an M-16A1 on full auto with no gas rings on the bolt to see if it would. Worked like a champ. A little info I purposely left out. Hence my questions in the OP.
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Old May 3, 2010, 11:10 AM   #16
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Hatcher mentioned that there was a sort of fad between the wars wherein every undiagnosed problem was blamed on headspace as a matter or routine. It didn't matter what the actual cause was. If it was mysterious, it was a headspace problem. I think the same thing may have developed regarding gas rings and the bolt carriers for the AR platform? Your description makes it sound like they replaced the bolt carrier and maybe the rings? The carrier could have been defective, I suppose, but without having it in hand to gauge, we'll never know? If the guy who fixed the upper found some embarrassing problem with the gas system that should not have got past inspection, you will never hear about it.

Old Grump gave you a version of a method that is useful for a number of things. I mix up Ed's Red, just to have a formula, and keep it in a gallon paint can. Immediately after shooting, I dip the carrier group in and run a wet patch of it through the bore. Same with a 1911 slide and barrel.

Carbon hardens over time. If you get a carbon softening solvent on a carbon deposit before it gets hard it is a lot easier to clean off later. There is a long diatribe on this topic by a former Aberdeen Proving Grounds employee, in post 25, here. A commercial preparation that will soften even hardened carbon overnight is Gunzilla.
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Old May 3, 2010, 02:28 PM   #17
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I picked up one of these critters: http://www.gngtools.com/ and polish the tail when cleaning.
I'm pretty anal about keeping the bolt clean and wet too. I have both Gunzilla and CLP on my bench. The GF refuses to use anything but Gunzilla do to her sensitive nose. I do any hard chemical cleaning when she's not around.
I want to thank the members for all the insight, tips and wisdom passed along in this thread.
The AR community beyond just me has been well served.
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