View Full Version : Can anyone help with this malfunction?
I recently aquired a used Colt 6721. It came with an unshrouded firing pin type half moon carrier, blue extractor insert, carbine buffer and gas rings which allowed the bolt to collapse on itself. Since its a used gun and ammo is pretty much unobtainable I decided to try to do some maintenance before I took it to the range. I put in a new BCM buffer spring and H-Buffer, new BCM gas rings and a new BCM extractor sping, black insert and O-ring.
I finally obtained some ammo and a few magazines so I tried to chamber a few rounds just to see how things were going and got some bad news.
http://i1308.photobucket.com/albums/s609/tomfiglia/Malfunction_zps6b67486d.jpg
http://i1308.photobucket.com/albums/s609/tomfiglia/Bulletdamage_zps351079c6.jpg
This happened only when hand cycling the action, never from a locked back bolt. It happened on one horrendous GI 30 round, one new old stock British 30 round and one brand new Colt 20 round. Occasionally it would completely fail for pick up a round from the magazine but I believe that may have only been from the old GI 30 round (I could be mistaken).
I was careful to make sure I was pulling the charging handle all the way back and not riding it forward and it locked back on all the empty magazines so it does appear to be clearing the bolt catch and ammo in the magazine. Also, after changing the gas rings, if I rode the charging handle on the gun while empty the bolt would not fully go into battery but would once I pushed the charging handle the rest of the way forward.
I tried removing the o-ring and nothing. I tried changing the gas rings back and it resolved the issue when riding the charging handle but I still experience the above malfunctions. I also switched back to the old buffer/spring and it seemed to experience less malfunctions, but they still occurred. The only thing I have not tried is going back to the old extractor spring/insert because I can't really see how that could be the problem, but who knows.
In addition to changing those parts I also tried removing the firing pin because I read that the unshrouded firing pin can catch on the notch of the hammer and someone on TOS suggested that as a quick way to check, it is not. (For anyone who has not tried to work their action with no firing pin, DO NOT EVER DO THIS. I had to remove the receiver extension to seperate the receivers and get the bolt out.) I then tried the proper test and removed the hammer, this also did not solve the problem. Finally, I tried tightening the magazine catch one turn which also had no effect.
So now I am at a loss. Any ideas? (Also the top image insists on being upside down for some reason, because that just seems to be my luck.)
Return the rifle to complete stock config and try again. If it functions as it should, upgrade one part at a time (don't know that you need the extractor O-ring) until you encounter the failure.
Thanks Sticks. I pretty much already did that except for the extractor spring/insert, but the rounds aren't getting anywhere close to the bolt face before getting hung up so I can't see how that would be the issue. The best results I had were going back to the original action spring/carbine weight buffer but this still wasn't perfect. I carry a 6920 at work and our carry condition is magazine inserted with an empty chamber. I've never had a single problem chambering a round with that. Also, if a brand new BCM action spring and H buffer don't work, doesn't it seem like there must be a deeper problem?
This is another picture which depicts the bolt position when the problem occurs.
http://i1308.photobucket.com/albums/s609/tomfiglia/Malfunction2_zpsb036fc74.jpg
Grumpy MSG
01-18-13, 06:28
Have you taken a good hard look at the area where the feed ramps on the upper receiver and the barrel are? You said it is used, parts in the bolt carrier sound wore out, that means some wear and tear. Maybe the tip of the bullet is actually catching the end of the barrel. Maybe the upper has M4 type feed ramps and the barrel doesn't(some parts already replaced).
Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.
You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
The feed ramps seem alright from what I can tell. Here's a picture. I learned how to post pictures so I'm going nuts with it.
http://i1308.photobucket.com/albums/s609/tomfiglia/Feedramps_zps8827ebe0.jpg
Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.
You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
This... I can't count the number of scratched up rounds that I've scratched up. I usually throw them in the plinker pile. Sucks when they're expensive match grade rounds...
SpankMonkey
01-18-13, 07:21
Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.
You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
This.
Guys, regarding the hand cycling, the original poster is saying that he can't even chamber the first round. That's a problem.
The feed ramps look fine. You can ignore the extractor, extractor spring, inserts/o-ring, and gas rings for now.
I'd focus on the magazines (which you already have done) and action spring(s). Is there a chance there is an issue with your buffer tube?
Can you describe or link to what you did when you checked the relationship of your notched hammer/bolt carrier/firing pin? Feel free to PM or email me.
Joe Mamma
Also, just out of curiosity, try a different bolt carrier. If possible, try a different design like a full auto/fully shrouded bolt carrier.
Joe Mamma
So if the OP puts a mag with a live round into the weapon and releases the bolt with the BOLT CATCH, it won't feed?
edit:
This happened only when hand cycling the action, never from a locked back bolt.
My original post stands. He's monkeying around and fixin to get an ND. I see nothing to suggest a problem with the weapon.
So if the OP puts a mag with a live round into the weapon and releases the bolt with the BOLT CATCH, it won't feed?
It does, but it should feed when using the charging handle (even with the mags fully loaded). Some people (and guns) have problems with that. But the OP said he does it all the time on a different AR gun with no problems. So I think he knows what he is doing in that regard.
This gun might work when live firing. But it's still not where it should be in my opinion.
Joe Mamma
the OP said he does it all the time on a different AR gun with no problems. So I think he knows what he is doing in that regard.
The idea that he's doing this nonsense "all the time" doesn't suggest to me that he knows what he's doing.
Since it looks like the OP covered almost all areas of a slow or under powered chambering by riding the CH I would address the buffer tube interior surface. Inspect the surface and see if any wear marks are visible due to the BCG rubbing. An easy way to rule this out is to loosen the buffer tube castle nut so the buffer tube can float. Now try to chamber the first round using your method described above.
uncle money bags
01-18-13, 10:49
Almost every time i have had a similar problem it was magazine related. Use a known good mag with a few rounds loaded first and if that works try fully loaded. Also check the straightness of the ch since it seems to be the one variable involved in the feeding issue.
I'm wondering if this could be mag related as well. OP, does the gun d this with all the magazines or just a certain one?
ETA: OP said it, I missed it
This happened only when hand cycling the action, never from a locked back bolt. It happened on one horrendous GI 30 round, one new old stock British 30 round and one brand new Colt 20 round. Occasionally it would completely fail for pick up a round from the magazine but I believe that may have only been from the old GI 30 round (I could be mistaken).
I suggest you get some dummy rounds. It's better to not tear up your ammo. It's also safer.
michael word
01-18-13, 12:52
Since he says that it feeds fine when using the bolt catch but not when using the charging handle, could there be something in the guide groves or a problem with the charging handle itself that is causing the bolt to slow down to the point that it wont feed? I would try cleaning out the recesses that the charging handle rides in and try it and then if that does not help I would try the charging handle from your other AR and see if that works, to see if this one is bent.
As much as it's going to not sit well with the OP, MarkM is right - the error most likely is user and magazine put together - at most a magazine with a worn mag catch slot is exacerbating it, but we need the OP to report if slingshotting the bolt magically fixes the problem.
michael word
01-18-13, 13:35
As much as it's going to not sit well with the OP, MarkM is right - the error most likely is user and magazine put together - at most a magazine with a worn mag catch slot is exacerbating it, but we need the OP to report if slingshotting the bolt magically fixes the problem.
OP has already stated that he tried 3 different mags, one being a new colt 20rd mag, all with same result.
Soooooo, have any of you had a moment when you realized you were probably an idiot? I did. I think markm is right and it sits just fine with me because I'm not really the sensitive type and it's free.
The more I thought about it I realized that, while I knew that cycling rounds through the magazine is not the same as shooting, it is also not the same as chambering a round from the magazine to put the rifle into action, which is what I meant by "doing it all the time." I tried putting all the new parts back in and, from an empty chamber, charging with the charging handle. I then removed the magazine, ejected the round and repeated until I emptied the new Colt magazine. There were no issues. So it seems like the only problem may be with me. I'm pretty happy about that being the case because I was thinking I should probably just unload this thing and pick up a sweet LWRC. ;)
I am left with one question, why would cycling the action cause a negligent discharge?
I recently aquired a used Colt 6721....
This happened only when hand cycling the action, never from a locked back bolt. ...
Also, after changing the gas rings, if I rode the charging handle on the gun while empty the bolt would not fully go into battery but would once I pushed the charging handle the rest of the way forward...
I missed a few things on first reading as well.
Charging handle?
Mags seating too deep in the lower?
M4 feed ramps on a rifle profile barrel?
Does this happen when there is more than one round in the mag?
lube the carrier riding surfaces?
hotrodder636
01-18-13, 16:59
The firing pin will hit the primer when cycling the bolt. However typically does not hot with enough force to ingnite the primer. Look at the rounds you "cycled" and see if you can see the small indent on the primers.....
Soooooo, have any of you had a moment when you realized you were probably an idiot? I did. I think markm is right and it sits just fine with me because I'm not really the sensitive type and it's free.
The more I thought about it I realized that, while I knew that cycling rounds through the magazine is not the same as shooting, it is also not the same as chambering a round from the magazine to put the rifle into action, which is what I meant by "doing it all the time." I tried putting all the new parts back in and, from an empty chamber, charging with the charging handle. I then removed the magazine, ejected the round and repeated until I emptied the new Colt magazine. There were no issues. So it seems like the only problem may be with me. I'm pretty happy about that being the case because I was thinking I should probably just unload this thing and pick up a sweet LWRC. ;)
I am left with one question, why would cycling the action cause a negligent discharge?
Hah, well, glad you made progress on pinning down the issue.
As for an ND, my thoughts on it, when you use live ammo for function testing it introduces the opportunity for it to be fired off simply due to a brain fart.
It's your BCG. Or maybe all that caked on carbon fouling... good god man... clean your rifle...
Yeah the bolt not closing on empty only happened when I really eased it closed and pushing the charging handle forward until it latches let's the bolt closed. After all the cycling I've been doing I can't get it to do that anymore. I didn't think it was really an issue but I wanted to give a full report. Has anyone experienced a discharge when cycling the action? Thanks for the help everyone, even though I may have just wasted a lot of your time.
Yeah the bolt not closing on empty only happened when I really eased it closed and pushing the charging handle forward until it latches let's the bolt closed. After all the cycling I've been doing I can't get it to do that anymore. I didn't think it was really an issue but I wanted to give a full report. Has anyone experienced a discharge when cycling the action? Thanks for the help everyone, even though I may have just wasted a lot of your time.
Sounds like it corrected itself. The above suggestion of cleaning?
I'd take a look at the gas tube and carrier key to make sure it's not tweaked and causing the binding [past tense].
As for firing when cambering, not that I know of, but it is a possibility if the ammo has soft primers. Double your chances with a dirty weapon if the firing pin gets bound in the forward position by carbon chunks or other grit. Why repeatedly take the risk?
Kind of a general rule to not mix live ammo and weapon tinkering at home at the same time. I reload, so I have all the dummy rounds I want for this kind of thing.
michael word
01-18-13, 18:00
Sounds like it corrected itself. The above suggestion of cleaning?
I'd take a look at the gas tube and carrier key to make sure it's not tweaked and causing the binding [past tense].
As for firing when cambering, not that I know of, but it is a possibility if the ammo has soft primers. Double your chances with a dirty weapon if the firing pin gets bound in the forward position by carbon chunks or other grit. Why repeatedly take the risk?
Kind of a general rule to not mix live ammo and weapon tinkering at home at the same time. I reload, so I have all the dummy rounds I want for this kind of thing.
If you look at how the bolt works, it is impossible for it to be stuck in the forward position. The bolt actively pulls the firing pin back when the bolt unlocks. Repeated chambering of rounds can also damage the internals of the primer, from the firing pin hitting it, causing a dud round.
Yeah the bolt not closing on empty only happened when I really eased it closed and pushing the charging handle forward until it latches let's the bolt closed. After all the cycling I've been doing I can't get it to do that anymore. I didn't think it was really an issue but I wanted to give a full report. Has anyone experienced a discharge when cycling the action? Thanks for the help everyone, even though I may have just wasted a lot of your time.
I have not. I learned on 1911s where hammer follow is a possible malfunction and it is a safety check. So diagnosing any issue is done with dummy rounds or nothing at all.
If you look at how the bolt works, it is impossible for it to be stuck in the forward position. The bolt actively pulls the firing pin back when the bolt unlocks. ....
Kind of a miss statement. The bolt moves away from the firing pin when it unlocks. Still slight potential for the pin to be wedged against the firing pin retainer or in the carrier. In actuality it will just damage the primer rather than firing the round, but weird shit does happen.
It's your BCG. Or maybe all that caked on carbon fouling... good god man... clean your rifle...
Yeah, that upper is asking for a few shots of brake cleaner.
Have you tried lube? Looks dry in every one of those photos.
Like I said, it seems like I was pretty much creating the problem since I can't get it to happen when charging from an empty chamber. The bolt, carrier and charging handle were all well lubed and the action spring was lightly lubed. I will definitely be doing a more thorough cleaning before I shoot the gun but I've been on midnights and my porch light is out. It's also freezing out there. Is brake cleaner good to use on the upper? We used to be told to use it on our Glocks at work and now they tell us not to. I'll definitely look at picking up a few dummy rounds. I don't usually cycle rounds but I did want to see how things were going after changing those parts and then sort of got caught up.
It's ashame that I pretty much had to make a dope of myself on the internet but I'm going to focus on the positives. I learned a lot of new things like not to EVER put the bolt carrier in the gun without the firing pin, how to remove and reinstall the hammer, how to remove, reinstall and stake the receiver extension and castle nut and how to post pictures. I also was forced to mount my new vise to my work bench and create a photobucket account so all of that is pretty good I guess.
One last question until I get this thing out to the range and come up with a million more, about how many times would to restake a castle nut onto the same end plate before replacing the end plate? Thanks for everyone taking the time to try to help me with all of this.
Like I said, it seems like I was pretty much creating the problem since I can't get it to happen when charging from an empty chamber. The bolt, carrier and charging handle were all well lubed and the action spring was lightly lubed. I will definitely be doing a more thorough cleaning before I shoot the gun but I've been on midnights and my porch light is out. It's also freezing out there. Is brake cleaner good to use on the upper? We used to be told to use it on our Glocks at work and now they tell us not to. I'll definitely look at picking up a few dummy rounds. I don't usually cycle rounds but I did want to see how things were going after changing those parts and then sort of got caught up.
It's ashame that I pretty much had to make a dope of myself on the internet but I'm going to focus on the positives. I learned a lot of new things like not to EVER put the bolt carrier in the gun without the firing pin, how to remove and reinstall the hammer, how to remove, reinstall and stake the receiver extension and castle nut and how to post pictures. I also was forced to mount my new vise to my work bench and create a photobucket account so all of that is pretty good I guess.
One last question until I get this thing out to the range and come up with a million more, about how many times would to restake a castle nut onto the same end plate before replacing the end plate? Thanks for everyone taking the time to try to help me with all of this.
Be sure to use non-chlorinated brake cleaner, spending an hour+ scrubbing and rubbing away makes no sense.
IMHO, if the castle nut doesn't index on the same spot as the previous stake, I'd call it good. Normally you could stake the castle nut at two places. I have an end plate on an AR that has had multiple stakes but it still structurally sound.
It did so I hit the original stakes with a punch which seemed to move a decent amount of metal back into the notches but I'll probably see if I can tighten it further and make new stakes or maybe I'll just get a QD end plate and kill two birds with one stone.
I wouldn't use brake cleaner on the bcg, as a mechanic I have found that it is harmful to rubber o rings.
As we have already seen.
1. Hand cycling is idiotic and serves no purpose.
2. You need to LUBE the weapon.
3. If you install new rings it's normal for the bolt to be tight.
4. Get rid of the O-ring. You don't need it.
motorolahamm
01-19-13, 17:13
Are you riding the charging handle forward?? Just thought I would ask may have been already asked. Sorry
The_Hammer_Man
01-19-13, 17:48
Seen this malf with new shooters a lot... they fail to draw the charging handle ALL the way to the rear... then scratch their heads when riding the charging handle doesn't fix things.
I know this thread is long dead, but it kills me when I do a search and find a thread like this with final no update. I finally scrounged up enough ammo/time to get the rifle out to the range. The final answer is hand cycling is, in fact, stupid and so am I.
I realize that 200 rounds isn't a torture test, but I tried a variety of .223 and 5.56 ammo and everything from brand new PMags to a beat to hell Adventureline that spits rounds if you tap the bottom. Every single round fed and ejected perfectly. There was nothing wrong with this gun at all.
I now want to thank everyone who took the time to try to solve my made up problem, particularly markm who called it right away.
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