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Posted: 1/24/2018 3:09:02 PM EDT
[#1]
damn, you have good eyes, i would have never noticed that. is there corresponding marks on the bolts?
my only guess is maybe a function thing, with how the AR platform cycles in general? |
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Posted: 1/24/2018 3:31:17 PM EDT
[#2]
tolerance stacking
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Posted: 1/24/2018 3:33:10 PM EDT
[#3]
Lol. I noticed once a long time ago and is just one of those things I look at now.
The bolt looks fine there is some finish wear on the lugs that correspond with area but that is it. Some of parkerization is rubbed off. They are not bashed up or anything. |
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Posted: 1/24/2018 3:34:46 PM EDT
[#4]
Are you talking about the mark on the actual face of the barrel extension? If so, you will notice that is the exact shape of the face of your bolt carrier. Its quite obviously making contact with the extension.
Not sure exactly which marks you're referring to tho |
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Posted: 1/24/2018 3:52:02 PM EDT
[#5]
are you referring to the marks circled in red?
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Posted: 1/24/2018 3:54:16 PM EDT
[#6]
Front of the barrel extension, as stated -two posts- above. To add, it means you "choot it"
I don't think you are talking about the tool marks (primarily seen on the lugs). Are you? Edt: -- |
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Posted: 1/24/2018 4:07:29 PM EDT
[#7]
Quote HistoryQuoted:
Front of the barrel extension, as stated -two posts- above. To add, it means you "choot it" I don't think you are talking about the tool marks (primarily seen on the lugs). Are you? Edt: -- |
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Posted: 1/24/2018 4:09:47 PM EDT
[#8]
Quote HistoryYes, those. I am just curious because the barrel extensions are lined up perfectly in the receivers. Like I said, just curious. I never could figure it out why it happens to some and not the others.
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Posted: 1/24/2018 9:01:48 PM EDT
[#9]
The front of the carrier always contacts the extension. That is what causes bolt bounce. There is always a little bolt bounce, even in semi. You just do not notice it. Craig
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Posted: 1/24/2018 9:23:56 PM EDT
[#10]
I appreciate the feedback. Like i said I am not talking about the bolt hitting the chamber face. I was just wondering about the 2 spots on the left 2 lugs (looking at the picture) of the barrel extension.
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Posted: 1/25/2018 12:42:23 AM EDT
[#11]
Quote HistoryThank you. Yes, those are marks I was talking about. Some rifles of mine have it and others don’t but they are all in the same spot.
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Posted: 1/25/2018 12:49:30 AM EDT
[#12]
Quote HistoryQuoted:
Thank you. Yes, those are marks I was talking about. Some rifles of mine have it and others don’t but they are all in the same spot. Quote HistoryQuoted:
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Posted: 1/25/2018 12:55:46 AM EDT
[#13]
It's dirty as hell because I haven't bothered to clean it in a long time, but here's a picture of one of my uppers. I built it using a Colt SOCOM barrel and a Colt bolt. It doesn't show the damage that yours does. I also checked two of my other uppers. A factory built Colt upper and a factory built SR-15 upper. None of them have this issue, so I'm not sure why you have so many that do. You mentioned that yours were all bought from a reputable company. Are all three uppers from the same company?
ETA: The more I study your pic, the more obvious it becomes that your bolt lugs are contacting the barrel extension on the way in. I wouldn't like that and I'm glad none of mine share this issue. |
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Posted: 1/25/2018 1:00:15 AM EDT
[#14]
Quote HistoryQuoted:
It's dirty as hell because I haven't bothered to clean it in a long time, but here's a picture of one of my uppers. I built it using a Colt SOCOM barrel and a Colt bolt. It doesn't show the damage that yours does. I also checked two of my other uppers. A factory built Colt upper and a factory built SR-15 upper. None of them have this issue, so I'm not sure why you have so many that do. You mentioned that yours were all bought from a reputable company. Are all three uppers from the same company? https://s14.postimg.org/maz0kr8rl/20180124_235206.jpg |
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Posted: 1/25/2018 1:03:10 AM EDT
[#15]
Quote HistoryQuoted:
Good God hit that thing with some brake cleaner! Quote HistoryQuoted:
Quoted:
It's dirty as hell because I haven't bothered to clean it in a long time, but here's a picture of one of my uppers. I built it using a Colt SOCOM barrel and a Colt bolt. It doesn't show the damage that yours does. I also checked two of my other uppers. A factory built Colt upper and a factory built SR-15 upper. None of them have this issue, so I'm not sure why you have so many that do. You mentioned that yours were all bought from a reputable company. Are all three uppers from the same company? https://s14.postimg.org/maz0kr8rl/20180124_235206.jpg 
400 rounds of M855 and about 120 of Tula went through that this past Sunday. I like leaving them dirty. 
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Posted: 1/25/2018 11:18:23 AM EDT
[#16]
Quote HistoryQuoted:
400 rounds of M855 and about 120 of Tula went through that this past Sunday. I like leaving them dirty. |
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Posted: 1/25/2018 11:41:44 AM EDT
[#17]
Factory assembled gun. I have 2 and have had 3 from the same company that all showed corresponding marks. I sent an email with pics off when I first noticed it in one of my guns years ago and was told it was good to go. The barrel is lined up perfectly so I am not sure why the bolt would be rubbing there.
Not sure if it is good form to disclose company name on public forum. |
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Posted: 1/25/2018 11:42:57 AM EDT
[#18]
Also. The odd part is that none of the other lugs have any marks. I would think if the bolt was hitting enough to cause dings, the other lugs would to
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Posted: 1/25/2018 12:23:58 PM EDT
[#19]
Here is a pic of the extension. You can see that it is line up. Also a picture of the bolt where there some finish wear on a corresponding bolt lug.
https://imgur.com/a/hYiD8 And yes all from the same company spanning several years. |
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Posted: 1/25/2018 12:37:34 PM EDT
[#20]
Quoted:
Also. The odd part is that none of the other lugs have any marks. I would think if the bolt was hitting enough to cause dings, the other lugs would to Quoted:
Here is a pic of the extension. You can see that it is line up. Also a picture of the bolt where there some finish wear on a corresponding bolt lug. https://imgur.com/a/hYiD8 And yes all from the same company spanning several years. |
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Posted: 1/25/2018 1:26:01 PM EDT
[#21]
Quote HistoryQuoted: If you have marks on the corresponding bolt lugs, then my guess is those two lugs are making contact with the barrel extension lugs when the bolt is sliding past them while going into battery. The bolt isn't dinging the face of the extension lugs on the way out, so it seems to me they're doing it on the way in. eta: it is not a huge ridge but you can feel a little spot where the metal is raised |
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Posted: 1/25/2018 1:36:21 PM EDT
[#22]
Quote HistoryQuoted: That is a though except the metal that has been displaced is pushed up instead of down, indicating that the force is coming from something sliding up or impacting on the side. By pushed up, I mean you can feel a little ridge with your nail on the front face of the lugs, not the sides |
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Posted: 1/25/2018 2:25:54 PM EDT
[#23]
I appreciate the advice. I don’t mean to sound like a dick but I have done all that. I can’t see any contact at all when manually sliding the bcg back and forth. I checked several times. Again thanks for the responses.
I am guessing it is fine since it is working fine. Could have been from a reaction rod or something if the company uses them? I guess that would explain bolt finish wear though. |
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Posted: 1/25/2018 5:12:43 PM EDT
[#24]
Sorry, but does anyone else have an opinion on why this is? I thought it was relatively normal considering the manufacturer said it was normal.
If this isn’t normal do you think it is anything to be concerned about? |
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Posted: 1/25/2018 5:53:27 PM EDT
[#25]
Looks like normal wear to me, im no expert by any means but ive been shooting ARs for the last 6 years or so and i personally would not worry about it. the only question i have for you is, does it run? if it does then just shoot it and have fun with it. you should see the lugs on my 7.5".
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Posted: 1/25/2018 6:11:58 PM EDT
[#26]
Quote HistoryQuoted:
It's dirty as hell because I haven't bothered to clean it in a long time, but here's a picture of one of my uppers. I built it using a Colt SOCOM barrel and a Colt bolt. It doesn't show the damage that yours does. I also checked two of my other uppers. A factory built Colt upper and a factory built SR-15 upper. None of them have this issue, so I'm not sure why you have so many that do. You mentioned that yours were all bought from a reputable company. Are all three uppers from the same company? https://s14.postimg.org/maz0kr8rl/20180124_235206.jpg ETA: The more I study your pic, the more obvious it becomes that your bolt lugs are contacting the barrel extension on the way in. I wouldn't like that and I'm glad none of mine share this issue. |
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Posted: 1/26/2018 1:37:13 AM EDT
[#27]
OP:
Funny you post that as I have always wondered about this sort of thing with AR's in that multilug barrels have that many more potential contact spots. I've never looked for this type of contact but would not be surprised to find that it is common for one or more locking lugs to nick the lug seats on the way in. I have never known anyone who actually looked for it! |
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Posted: 1/26/2018 8:56:38 AM EDT
[#28]
You know what causes that?
You shooting them..... Metal parts....moving against metal parts.... Don't ever take your car engine apart..... |
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Posted: 1/26/2018 10:16:08 AM EDT
[#29]
Quote HistoryQuoted:
Sorry, but does anyone else have an opinion on why this is? I thought it was relatively normal considering the manufacturer said it was normal. If this isn’t normal do you think it is anything to be concerned about? Quote HistoryQuoted:
Sorry, but does anyone else have an opinion on why this is? I thought it was relatively normal considering the manufacturer said it was normal. If this isn’t normal do you think it is anything to be concerned about? I bet it isn't uncommon. As for "normal", I don't know. It's not "good" in that the lugs ideally should enter the spaces between the lug seats without striking any part of the seats themselves first, but I think you know that. I'm glad you posted as all this sort of thing I find interesting. I'd be curious to see just how bad it could get in a sloppily made gun with ragged tolerances. There are some limiting dimensions that would prevent full-on abutment of the lugs against the lug seats, but I imagine there could be worse than what you have posted here. Quoted:
I appreciate the advice. I don’t mean to sound like a dick but I have done all that. I can’t see any contact at all when manually sliding the bcg back and forth. I checked several times. Again thanks for the responses. I am guessing it is fine since it is working fine. Could have been from a reaction rod or something if the company uses them? I guess that would explain bolt finish wear though. |
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Posted: 1/26/2018 11:31:47 AM EDT
[#30]
I've had this happen to a Spikes upper and BCM upper in the past. I immediately sold them(buyer was aware).
I have many other AR's that do not do this and I am not willing to live with one that does. |
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Posted: 1/26/2018 9:39:16 PM EDT
[#31]
Interesting comments so far. It may not be the norm but it happens. I haven’t named the company because there is no reason to if it is not a huge problem.
I did some googling if barrel extensions and sure enough some images show a some marks like that. There were others that were beat to hell and were obviously going to fatigue parts early. Still there were images of some extensions that had smaller marks like mine and no one seemed concerned about them. It is funny how we such a spectrum. Some say it is ok and others not so much. Thanks for the feedback and opinions thus far |
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Posted: 1/26/2018 10:22:27 PM EDT
[#32]
Quoted:
Looks like normal wear to me, im no expert by any means but ive been shooting ARs for the last 6 years or so and i personally would not worry about it. the only question i have for you is, does it run? if it does then just shoot it and have fun with it. you should see the lugs on my 7.5". Quoted:
Gross lol. Do you shoot it suppressed? That's what mine look like after a couple hundred rounds suppressed. |
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Posted: 1/26/2018 10:24:38 PM EDT
[#33]
Nitpicking. Even in the excellent large picture I totally glossed over those little peens, looking for some serious damage. Some guns turn out better than others. Its possible that the marks are handling marks from before the gun was assembled. Keep your eye on it. I don't think it will get worse but you should know after about 500 rounds.
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Posted: 1/26/2018 10:26:14 PM EDT
[#34]
Quote HistoryQuoted:
Nitpicking. Even in the excellent large picture I totally glossed over those little peens, looking for some serious damage. Some guns turn out better than others. Its possible that the marks are handling marks from before the gun was assembled. Keep your eye on it. I don't think it will get worse but you should know after about 500 rounds. 
There's corresponding marks on the bolt face, so it isn't from "handling". It's not normal and something is out of spec if it's happening. Whether it's a big deal or not is up to the OP or the bolt if it decides to shear a lug early. Doubtful, but if the problem continues to get worse, eventually it will impart a ton of stress on the lugs. Consider the bolt's forward velocity each time it makes contact, especially if it gets worse and they start making even more contact. If this was my upper, I'd swap bolts just for testing purposes. If I had 3 out of 5 uppers from the same company doing this, I would immediately stop buying from them. Again, somethings out of spec and it should be caught and corrected. |
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Posted: 1/27/2018 12:01:39 AM EDT
[#35]
Quoted:
So I have noticed out of the 5 ARs I have owned 3 have had these marks. They are always in the same spot. All bought from reputable company over the past 8 years or so. What causes this? I haven’t had any issues with any of the guns. I own 3 still. 2 have the marks and 1 doesn’t. Marks are on the two left lugs. You can see the shiny part. https://imgur.com/a/YRtiy There is some finish wear on the bolt lugs that correspond but it is just finish wear. Oops, my bad |
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Posted: 1/27/2018 12:56:46 AM EDT
[#36]
Quote HistoryQuoted: OP: I bet it isn't uncommon. As for "normal", I don't know. It's not "good" in that the lugs ideally should enter the spaces between the lug seats without striking any part of the seats themselves first, but I think you know that. I'm glad you posted as all this sort of thing I find interesting. I'd be curious to see just how bad it could get in a sloppily made gun with ragged tolerances. There are some limiting dimensions that would prevent full-on abutment of the lugs against the lug seats, but I imagine there could be worse than what you have posted here. Is there some reason you aren't posting the maker? |
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Posted: 1/27/2018 12:58:25 AM EDT
[#37]
Quote HistoryQuoted: Handling marks?
There's corresponding marks on the bolt face, so it isn't from "handling". It's not normal and something is out of spec if it's happening. Whether it's a big deal or not is up to the OP or the bolt if it decides to shear a lug early. Doubtful, but if the problem continues to get worse, eventually it will impart a ton of stress on the lugs. Consider the bolt's forward velocity each time it makes contact, especially if it gets worse and they start making even more contact. If this was my upper, I'd swap bolts just for testing purposes. If I had 3 out of 5 uppers from the same company doing this, I would immediately stop buying from them. Again, somethings out of spec and it should be caught and corrected. |
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Posted: 1/27/2018 1:06:07 AM EDT
[#38]
Quote HistoryQuoted: I notified the company they said it was good to go. A ton of people have their rifles. So I’d imagine they have been lasting a while or this board would be going nuts. 
The small amount of problems vs the quantity they sell is a testament to their quality. |
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Posted: 1/27/2018 1:28:33 AM EDT
[#39]
I hate these threads. Why bother unless you name the company. It’s obvious it bothers you on some level it you would have said oh well and never gave it a second thought.
Clearly that’s nit normal and it’s probably not anything good is going to come of it. Between this and the couple other threads I wonder wtf is going on at BCM lately. |
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Posted: 1/27/2018 2:12:50 AM EDT
[#40]
Does not bother me too much. I was just curious why it seems to be on some rifles. Like I said, company said it was good to go. What I find most interesting is how some people think it is fine and some don’t.
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Posted: 1/27/2018 2:50:56 AM EDT
[#41]
It's the front edge of the bolt lugs hitting the barrel extension during chambering.
Usually see that in cases where the extension is slightly rotated in the upper after barrel installation. |
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Posted: 1/27/2018 2:51:12 AM EDT
[#42]
In some weapons, things have to wear in by creating a little (or sometimes big gouges). Basically a "mating" process which stops after so long.
I would say if after 1000 rounds, you notice the gouges getting deeper, then it is something to be of concern. Otherwise, some firearms have "mating" process that occurs. I had a Bersa Thunder years ago, and there was a very deep gouge on the slide where the trigger reset went into. After about 1k rounds through it, I noticed it settled. I asked the company about it, and they said it was normal, but if it gets any deeper then it is something to be of concern. My point here is that there are some tolerance differences, and in some cases, it has to settle. If it gets any bigger, deeper, or wider, or cracks the lugs off the bolt, then that is something to be of concern. Only way to keep a firearm free of any wear is by never firing or dry cycling it. |
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Posted: 1/27/2018 4:13:17 AM EDT
[#43]
Quote HistoryQuoted:
It isn't normal wear. The faces of the bolt lugs should never be making contact with the extension lugs on their way into battery. Will it shorten the life of the bolt? Maybe, maybe not. Depends on how much contact there is. Although, any contact made is adding undue stress to the lugs. The bolt face contacting the extension definitely isn't built into the design. I would like to know who the manufacturer is. Yes, it gets dirty quick. Quote HistoryQuoted:
Quoted:
Looks like normal wear to me, im no expert by any means but ive been shooting ARs for the last 6 years or so and i personally would not worry about it. the only question i have for you is, does it run? if it does then just shoot it and have fun with it. you should see the lugs on my 7.5". Quoted:
Gross lol. Do you shoot it suppressed? That's what mine look like after a couple hundred rounds suppressed. |
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Posted: 1/27/2018 12:12:08 PM EDT
[#44]
Quote HistoryQuoted:
It's the front edge of the bolt lugs hitting the barrel extension during chambering. Usually see that in cases where the extension is slightly rotated in the upper after barrel installation. |
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Posted: 1/28/2018 1:16:37 PM EDT
[#45]
Quote HistoryQuoted:
Sorry, but going to have to disagree with you. Too many variables. Bottom line is not all componets wear the same way, yes I know there are tolerances but everything wears differently, some plateforms are harder on some more so than others. Quote HistoryQuoted:
Quoted:
Quoted:
Looks like normal wear to me, im no expert by any means but ive been shooting ARs for the last 6 years or so and i personally would not worry about it. the only question i have for you is, does it run? if it does then just shoot it and have fun with it. you should see the lugs on my 7.5". Quoted:
Gross lol. Do you shoot it suppressed? That's what mine look like after a couple hundred rounds suppressed. Disagree all you want. There isn't "too many variables" and I already stated my opinion and posted pics of my KAC upper without this damage. The face of the bolt lugs aren't supposed to slam into the extension lugs on their way in and that's the end of it. How could you consider face to face contact between the bolt and barrel extension normal? It may not be that big of an issue for the OP since It's making minimal contact, but trust me, that isn't happening by design.
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Posted: 1/28/2018 1:29:57 PM EDT
[#46]
Caused by tolerance stacking. Factors involved include barrel alignment pin notch, gas key/charging handle channel width (where the cam pin rides in the upper) and of course cam pin width.
If the barrel truly looks centered (which it is not based on the pics), not likely your alignment pin notch, but don't dismiss this entirely. If the cam pin running area in the upper allows too much play of the cam pin, only real option is replacing the upper if you really don't want these marks. If the cam pin is too narrow on it's own, that's an easy replacement. If it's a stacked factor of all three, then a minor change in any one of them can alleviate this issue. Easiest to do is to find a cam pin with a wider head followed by disassembling the upper and re-torqueing on the barrel. How you do this will dictate the direction the barrel wants to "rest" when done. Use a reaction rod system and the barrel will naturally cant to the right (OPV). Use receiver clamshell and the receiver will naturally cant to the left. If re attaching the barrel clears the issue up but the feed ramps don't appear aligned, no worries. Not a big deal. There's always a chance the feed ramps were machined slightly offset as well, and if the builder used the feed ramps as their alignment "gauge", then the whole thing would be off. Personally, i'd re-torque the barrel to clear this issue up. I wouldn't allow this kind of work out of my shops over seas and I certainly don't allow it when I work on guns for people here at home either. |
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Posted: 1/28/2018 2:32:09 PM EDT
[#47]
Quote HistoryQuoted:
Caused by tolerance stacking. Factors involved include barrel alignment pin notch, gas key/charging handle channel width (where the cam pin rides in the upper) and of course cam pin width. If the cam pin running area in the upper allows too much play of the cam pin, only real option is replacing the upper if you really don't want these marks. If the cam pin is too narrow on it's own, that's an easy replacement. . |
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Posted: 1/28/2018 2:50:47 PM EDT
[#48]
Weird. Not sure I'd be comfortable with that. Over a few thousand rounds, I could see that being a problem.
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Posted: 1/28/2018 2:52:57 PM EDT
[#49]
Interesting. I've never heard about this problem before.
And... now I know how to fix it. |
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Posted: 1/28/2018 3:15:09 PM EDT
[#50]
Quote HistoryQuoted: This was my experience w/ Colt M4 SOCOM upper with a used carrier and cam pin. I had exactly the same wear as the pics above. Changed out to a new cam pin/ carrier and problem stopped. My case it wasnt the upper, it was the cam pin channel in the carrier made the bolt wobble more than it should have. Meaning that there is a larger tolerance stacking issue to your problem and you fixed a single aspect of the stack. It's a temporary fix, but a fix none-the-less. Did you get comparative measurements on the carrier cam channel for reference? On another note, a good test for this issue is to pull the bolt to the rear without a magazine or ammo, then slowly ride the bolt forward and push the bolt rearward with a tool through the ejection port. Observe how much rotational play of the bolt is allowed and then slowly let it enter the barrel extension, noting where it is touching, if at all. |
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