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Old August 21, 2012, 09:35 PM   #1
GI Sandv
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Stuck Bolt Carrier Group

I just bought a fully assembled upper from a guy who builds guns locally. I bought one with a nickel boron bcg thinking that I wouldn't run into too many issues with cleaning, dirty loads, etc. Lo and behold, I loaded my first mag with three rounds to zero the gun in and, "click." Failure to fire. I attempted to eject the round but the charging handle would only pull back about 1/4 inch. I dropped the mag, attempted the charging handle and again no luck. I tried using the forward assist to no avail as well. After attempting this a few times I called another guy at the range over and we pulled from two ends of the gun, me from the barrel and him from the charging handle. This finally worked. The primer had a scuff mark where the firing pin had hit but it wasn't even a full depth dent. I loaded the round back into the mag with a different round on top this time. I released the charging handle, selected fire, and "bang." It fired all three rounds this time, including the one that had failed to fire previously.

Unfortunately, this happened a few more times. If I remember correctly, each time it happened was from me pulling the charging handle all the way back and releasing, rather than locking it back and hitting the bolt release. Eventually I just pulled the upper off, tried to pull the bolt as far back as it would go (1/8 - 1/4 inch) in order to avoid accidentally hitting the firing pin, and I would pry the bolt back with a flat head screwdriver. Sometimes it was more stuck than others. But in every case I either had to pry the bcg loose or have another person help me pull the charging handle while I pulled on the barrel. (Don't worry, the barrel was still pointing down range and not at any of my body parts.)

Eventually I took the bcg apart and was able to easily wipe away any and all fouling from the few rounds I'd already fired. However, on the back side of the bolt (not the bcg), on the rounded/sloped part just behind the two c-rings where there's often a good amount of caked carbon on well used bolts, there was a solid deposit of fouling and copper. I was surprised because all of the rest of the bolt wiped clean with a rag, just as advertised with these nickel boron carriers and bolts. I didn't have the appropriate tools to clean this off so I left it, but wiped it with some CLP and ran a rag over it, which only took off a little bit of it. I'm not sure whether this would be resulting in the carrier and rounds being jammed in the chamber or not. The only other things that come to mind are that the extractor pin is pushing too hard against the round, creating extra perpendicular pressure against the chamber, or that my brand new p-mags are pushing on the carrier in a strange way. But removing the mags doesn't change anything. I'm not sure whether it could be the bolt itself or not, since I don't have this problem unless there's a round in the chamber. Could it just be part of the breaking in process? I only put about 40 rounds through it today and for what it's worth, I was using American Eagle 55gr FMJ rounds.

Any thoughts would be greatly appreciated. I plan to go back to the range tomorrow and see what I can figure out. After that, I'm calling the guy who built the upper.
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Old August 21, 2012, 09:41 PM   #2
chris in va
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I'd have a close look at the chamber face. A similar incident happened at the range last week and the guy had some debris stuck in the locking lugs. I had a blown primer do the same thing to mine.
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Old August 21, 2012, 09:47 PM   #3
RamItOne
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Have the other guy stand on the business end next time

"After attempting this a few times I called another guy at the range over and we pulled from two ends of the gun, me from the barrel and him from the charging handle."




Clogged locking lugs, poorly lubed bcg or worse the specs of the bcg might be off slightly
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Old August 21, 2012, 10:08 PM   #4
Marquezj16
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This is not a break in issue. Contact who you purchased it from. See if they are willing to fix it to make it right (don't know if he guarantees his work).
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Old August 21, 2012, 10:32 PM   #5
DnPRK
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Did you lube the BCG until it drips?

Gas guns need lube. New gas guns need lots of lube.

After a couple hundred rounds, the rough surfaces will burnish and you will be able to reduce the amount of lube.
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Old August 22, 2012, 02:12 AM   #6
Palmetto-Pride
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Well it sounds like the bolt is not wanting to rotate and unlock from the chamber. (I had my M&P15 do this occasionally when using steel case ammo I never could figure out what it was about the steel cased ammo that was causing the problem) Have you tried to manually run some rounds thru it with a full magizine to see if any get stuck? Also have you tried to lightly let the charging handle go forward just to see how easy it is for a round to go into battery? You may have to lightly push on the FA, but you shouldn't have to jam on it to get into go into battery.
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Old August 22, 2012, 07:47 AM   #7
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Quote:
on the back side of the bolt (not the bcg), on the rounded/sloped part just behind the two c-rings where there's often a good amount of caked carbon on well used bolts, there was a solid deposit of fouling and copper.
That's not normal for a 'new' BCG. I agree with Palmetto-Pride on the bolt not fully locking in place. Can you rotate the bolt in the carrier by hand? How much resistance is felt?

Clean, oil and retry with brass case ammo.
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Old August 22, 2012, 08:06 AM   #8
UtopiaTexasG19
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I always disassemble new BCG's, clean and over oil, then sit in front of the tv for an hour or so and manually rotate, push and pull on the bolt in the carrier over and over until the movement is smooth and without any rough spots. Well, I am sitting in front of the tv anyway doing nothing. This slightly wears in the parts and gas rings and makes the initial rounds chamber and eject easier. It is surprising sometimes how stiff a new BCG can be. I also oil liberally for the first 500 or so rounds. Next time a cartridge gets stuck in the chamber and will not eject learn how to "mortar" the rifle rather than have someone else hold the barrel. If done correctly it will not damage the rifle and is a much safer way to get a stubborn round out. Take the gun back to the builder and see what he/she says about the problem.
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Old August 22, 2012, 09:08 AM   #9
GI Sandv
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Thanks for the replies. Because it's a nickel boron bcg, I was hoping this would be the magic solution that prevented me from having to lube anything. Perhaps at least a little between the carrier and bolt, as well as a tiny bit in the star chamber near the lugs will help, at least until the rifle settles in a bit. At this point in my life, I had thought that I had learned to always inspect new equipment before trying to use it. But somehow I failed to notice the buildup on the backside of the bolt. Stupid failure on my part, although I don't know that it would have changed anything.

Does anyone on here with a nickel boron bcg have any thoughts on where, how much, and when to lube this? It's supposed to operate without lube, but my car is also supposed to get 19mpg, which never happens. Also, for those with nickel boron, do the surfaces of your carrier and bolt look the same? I just noticed that my bolt has a much more matte finish than the carrier does, which makes me wonder whether the builder used stainless or chrome rather than nickel boron for the bolt, and just used a nickel boron carrier. In either case, I'll call him and ask whether he runs into this sort of problem with his new builds, and I'll ask about the bolt as well.

To answer some of the questions raised: rotating the bolt in the carrier is possible although stickier than I am used to (in well-worn service M4s). There's no significant amount of debris in the locking lugs, unless this is something that you couldn't discern simply by looking at it. I was only using brass ammo yesterday. And as for manually running rounds through it, I did attempt to eject live rounds from the chamber with a magazine in but the bcg wouldn't come back. So, I just fired and it cycled then, but only while firing. I didn't want to induce another jam if I didn't have to. Just now, with the upper detached, I was able to manually cycle the bolt in and out of battery without any problems. Doing it over and over for two or three minutes was pretty easy and the bolt was rotating fine.

And thanks, Tex, for the recommendation for mortaring. I had never run across this technique but will try it out next time I get a jam like this. (I had hoped to try again today, but now my shoulder seems to be out of battery and until that gets worked out, there will be no shooting.)
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Old August 22, 2012, 12:16 PM   #10
Basement-Gunsmith-Z
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Take the advice from everybody that posted. In your post i noticed you said you pulled the barrel and someone else pulled the charging handle. The easy way to do this is to get on your knees, lay the stock flat against the floor, make sure the stock is fully retracted, grab the charging handle with one hand, and the forend with the other. Than, lift the rifle up about 1 foot or so and bring it onto the ground with considerable force. The bcg should come right back. I know it seems a bit harsh, but it works, it's what the military has been doing for years. If it has a round chambered point the barrel in a safe direction. Use common sense. Oh and yes i know this is referred to as "mortaring". but i thought i would post this as a detailed guide.
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Old August 22, 2012, 02:24 PM   #11
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Can't say I'm in favor of "mortaring" the rifle. (never heard this term before today), but slamming the butt into the ground to get the bolt carrier unstuck seems like something to be done only when other people are shooting at you!

Also using a screwdriver to "pry" the bolt loose makes me cringe.

Back when I had an AR (and years after the Army trained me to work on the M16) when there was a stoppage, one that the forward assist would not chamber, one popped both pins, removed the upper, and used a piece of wood and a small hammer to tap on the rear "ring" portion of the bolt carrier. I've done it many times (had a large batch of "bad" ammo). It works, does no harm to the rifle, and to my eyes, beats the hell out of slamming it on the ground!

BTW, that same "bad" ammo ran through my Mini14 like poop through a goose.

One of the worst features of the AR design is its charging handle. Works ok when everything is fine, but when something goes wrong, no leverage at all. That big clunky op rod handle on the M14, Garand, and Mini14 has some advantages the AR does not.
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Old August 22, 2012, 03:17 PM   #12
UtopiaTexasG19
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According to my brother, our Vietnam veteran, "mortaring" was unofficially adopted during fire fights when someone was shooting at you and your life was on the line. Yes, maybe not the best way to treat your rifle during peace time, but still a handy method to practice and know in a pinch.
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Old August 22, 2012, 03:45 PM   #13
Coltman 77
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Great advice from UtopiaTexasG19:

Quote:
I always disassemble new BCG's, clean and over oil, then sit in front of the tv for an hour or so and manually rotate, push and pull on the bolt in the carrier over and over until the movement is smooth and without any rough spots. Well, I am sitting in front of the tv anyway doing nothing. This slightly wears in the parts and gas rings and makes the initial rounds chamber and eject easier. It is surprising sometimes how stiff a new BCG can be. I also oil liberally for the first 500 or so rounds. Next time a cartridge gets stuck in the chamber and will not eject learn how to "mortar" the rifle rather than have someone else hold the barrel. If done correctly it will not damage the rifle and is a much safer way to get a stubborn round out. Take the gun back to the builder and see what he/she says about the problem.
AR's need to be run well lubed. I also agree about taking it back to the seller asap and letting him make it right.

Good luck, keep us updated.
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Old August 23, 2012, 07:51 AM   #14
GI Sandv
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Well, despite my shoulder, I went to the range yesterday. I put another fifty rounds or so through the gun. I didn't have any issues with the bolt/bullet sticking and didn't have to practice my mortaring technique. The rifle shot fine, although I'm not so sure about myself. I hadn't done much of anything since the previous day except to slide the bcg in and out of the chamber about twenty or thirty times really quickly to make sure they were moving and functioning fine. I dabbed a tiny bit of clp around the bolt, inside the carrier, where the rings are. Don't know if that's what was needed or not, but as I said, it worked fine yesterday. I have yet to introduce this rifle to more rapid sequences of fire. At most, I shot three three-shot groups in two minutes. Otherwise it was three short groups with three to five minutes in between. Now that the kinks seem to be worked out, I'm hoping to test the reliability of this nickel boron bolt to see if it really runs dirty as all the manufacturers claim.

Thanks for all the replies.
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Old August 23, 2012, 06:30 PM   #15
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My rifles get some smoothing prior to shooting. I like to see the BCG slide into battery and lock by it's own weight when released into the unistalled upper from anything more than a 45* muzzledown angle. Up to this point in time, I've not had any problems achieving this with common milspec BCG parts.
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Old August 24, 2012, 02:59 PM   #16
Metal god
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?????????

Is/was the upper new ? If the upper had been used/fired before and they used steel cased ammo .

Carbon could have built up in the chamber and caused the brass to stick to the chamber walls .

Steel case ammo does not expand and seal the chamber as well as brass does . When this happens the gases and other crap (carbon) can leak into the chamber and build up . If you do not clean your chamber really ,really well after using steel cased ammo the softer brass can stick to the chamber walls . When this happens you can rip the rim off of the cartridge or break the extractor .

Now that being said , This normally happen when you switch from steel case to brass and the chamber is still hot . ( ie one mag has steel the next brass )

I can see it happening with a cold bore if there is alot of buid up in the chamber . Im not sure how many rounds of steel you would have to put down range without cleaning for this to happen . I would think it would be many hundreds if not a thousand or so .

If it was new did any body give it the go , no go test and test fire it .

Last edited by Metal god; August 24, 2012 at 10:08 PM.
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Old August 24, 2012, 04:49 PM   #17
GI Sandv
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Metal god,

I bought it from a guy who test fires all his rifles before he sells them. So, I'm certain that's where the carbon build-up came from. He told me he uses exclusively his own reloaded ammo, which I assume goes for test fires as well as his own rifles. I would think test firing only goes for a few, maybe twenty rounds at most. So, I'm still not sure why the big hunk of build-up was on the back side of the bolt. Nonetheless, after a wipe down and 100 or so rounds, everything's in good working order.
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Old August 24, 2012, 10:00 PM   #18
Metal god
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If he only fires his own reloads . That would meen that chamber has never seen a steel case . If that is indeed the case and he only fired a few rounds to test , carbon build up in the chamber was never the problem . Its always nice to exclude thing as being the problem .

As for build up on the bolt inside the carrier with so few rounds thru it ( hum )thats a real head scratcher for me .

( QUOTE ) However, on the back side of the bolt (not the bcg), on the rounded/sloped part just behind the two c-rings where there's often a good amount of caked carbon on well used bolts, there was a solid deposit of fouling and copper

It seems impossible for this to happen with the normal opperation of the gun . The only thing I can think of is when he put the BCG together some fouling and copper got trapped insinde the carrier when inserting the bolt, and that does not even sound right . I don't know maybe he had a dirty work area or something

Has anybody else ever seen fouling and copper insinde there BCG ? I would love to here that story and how it got in there .
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Old August 25, 2012, 04:42 PM   #19
Metal god
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I got it ( maybe )

Maybe there is/was a bur in the barrel at the gas port . When the bullet passes by the gas port , the bur shaves a little off the bullet and the gasses send it down the gas tube back into the BCG .

Thats the only way I can think of little bits of the bullet getting inside the BCG

Any other ideas ?

Last edited by Metal god; August 25, 2012 at 04:51 PM.
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