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Posted: 3/31/2016 2:49:06 PM EDT
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So, I've been told that my buffer tube is out about one thread too far out. And that might be correct. Supposedly the bolt should be sticking ahead of the port opening about 1/4" or somewhere there abouts when you pull back the charging handle all the way. I got the tube from PSA and it's a milspec tube. When I installed I went as far as I could without crushing the buffer retaining pin. So I figured that was correct. But the bolt is more like near flush with the port opening at the rear when pulling the charging handle all the way back.
I guess that is not optimal for ejection. Because I was concerned my upper is overgassed because it just poops the brass out at like 12:30 or 1:00. So either it's correct. Or I need to trim the tube if I want to keep the buffer retaining pin in. Has this happened with anyone else? Is there a source that deals with this issue? I searched the threads in here about building but none of them seem to cover this exact issue. I did actually turn the tube in one, left the retaining pin out and shot for function. It did seem to eject a bit more positively and a bit more to the right. Nothing dramatic, but a small improvement. I think. What say you guys about this? Anybody else run into this? |
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I've built a dozen or so ARs and have never had this issue...
I've always turned the tube until it sits just on top of the base (flat part) of the retaining pin but doesn't quite touch the pin itself. Every buffer tube I've assembled has been the same - if you crank it one more turn past this point, you crush the pin and it won't hold in the buffer and spring assembly...if you don't crank it enough, the pin will come flying out. It sounds like yours might be out of spec. Can you take pics? |
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I got the tube from PSA and it's a milspec tube. When I installed I went as far as I could without crushing the buffer retaining pin. So I figured that was correct. But the bolt is more like near flush with the port opening at the rear when pulling the charging handle all the way back. A good pic of the tube at its original depth and another of it one turn in, with the buffer retainer pin installed, would help a lot. If the tube doesn't index, then either the receiver extension threads on your receiver are mistimed, or the tube threads are mistimed, or the buffer detent hole was drilled out of its correct location. |
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i don't see how your buffer tube would cause your problem and I dont see that as a problem one turn in is no where near a 1/4 in and being under spring tension as you pull back would push your bcg forward and your brass shoot at 12:30 1:00 is the brass hitting the brass deflector I would think you need a different heavier buffer and or spring to fix the ejection pattern
Dan |
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I've built a dozen or so ARs and have never had this issue... I've always turned the tube until it sits just on top of the base (flat part) of the retaining pin but doesn't quite touch the pin itself. Every buffer tube I've assembled has been the same - if you crank it one more turn past this point, you crush the pin and it won't hold in the buffer and spring assembly...if you don't crank it enough, the pin will come flying out. It sounds like yours might be out of spec. Can you take pics? Your install is the same as my experience. Sounds like maybe his retaining pin hole may not be in the right place or not angled correctly? |
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A good pic of the tube at its original depth and another of it one turn in, with the buffer retainer pin installed, would help a lot. If the tube doesn't index, then either the receiver extension threads on your receiver are mistimed, or the tube threads are mistimed, or the buffer detent hole was drilled out of its correct location. Quoted:
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I got the tube from PSA and it's a milspec tube. When I installed I went as far as I could without crushing the buffer retaining pin. So I figured that was correct. But the bolt is more like near flush with the port opening at the rear when pulling the charging handle all the way back. A good pic of the tube at its original depth and another of it one turn in, with the buffer retainer pin installed, would help a lot. If the tube doesn't index, then either the receiver extension threads on your receiver are mistimed, or the tube threads are mistimed, or the buffer detent hole was drilled out of its correct location. You know what I should've done, is pushed down on the retaining pin, in the second, closer, postion. Because there is like a slope to the pin at the base and that might be part of the problem. It does look pretty far out in the position I had it originally: 
Sorry the pin isn't in there, I didn't think about pushing it down further at the time. 
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i don't see how your buffer tube would cause your problem and I dont see that as a problem one turn in is no where near a 1/4 in and being under spring tension as you pull back would push your bcg forward and your brass shoot at 12:30 1:00 is the brass hitting the brass deflector I would think you need a different heavier buffer and or spring to fix the ejection pattern Dan I'm not sure you have that part quite right. I do believe the back of the tube is stopping the BCG. It might be that you run our of room on the charging handle, but I think it's designed to bottom out right around the same length. When it's firing, it's definitely the back of the tube that stopping it. Because if you move your BCG with the upper off of your lower, with the CH closed the BCG will go much deeper into the upper. Or to the rear. I agree that part of the brass throwing is probably how it's sprung. Because using a 9mm buffer did change it some. But actually, I think screwing the tube in one more seem to help ejection almost more than the buffer. Possibly. More rounds went closer to 2 oclock than when I was shooting on Monday and seemed to be thrown a little further than what I remember. Although it could've been just the type of ammo. I should've shot the same exact rounds. But I was more concerned with .223 and 5.56 loads and that's what I took today. |
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You know what I should've done, is pushed down on the retaining pin, in the second, closer, postion. Because there is like a slope to the pin at the base and that might be part of the problem. It does look pretty far out in the position I had it originally: http://i343.photobucket.com/albums/o475/NomadABPos/2016%20guns/IMG_5254_zpsctghi277.jpg Sorry the pin isn't in there, I didn't think about pushing it down further at the time. Looks to me like you need one more turn from what you show in the top picture. Again, it should just barely miss hitting the point but fully retain the pin fully. http://i343.photobucket.com/albums/o475/NomadABPos/2016%20guns/IMG_5255_zpsen3ww1d3.jpg Quoted:
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I got the tube from PSA and it's a milspec tube. When I installed I went as far as I could without crushing the buffer retaining pin. So I figured that was correct. But the bolt is more like near flush with the port opening at the rear when pulling the charging handle all the way back. A good pic of the tube at its original depth and another of it one turn in, with the buffer retainer pin installed, would help a lot. If the tube doesn't index, then either the receiver extension threads on your receiver are mistimed, or the tube threads are mistimed, or the buffer detent hole was drilled out of its correct location. You know what I should've done, is pushed down on the retaining pin, in the second, closer, postion. Because there is like a slope to the pin at the base and that might be part of the problem. It does look pretty far out in the position I had it originally: http://i343.photobucket.com/albums/o475/NomadABPos/2016%20guns/IMG_5254_zpsctghi277.jpg Sorry the pin isn't in there, I didn't think about pushing it down further at the time. Looks to me like you need one more turn from what you show in the top picture. Again, it should just barely miss hitting the point but fully retain the pin fully. http://i343.photobucket.com/albums/o475/NomadABPos/2016%20guns/IMG_5255_zpsen3ww1d3.jpg |
| Yeah, it looks like that first one is barely over the pin. But it seems like they were made wide for that reason. Variance in tubes....... ????? I'm going to try pushing down the retaining pin in the new position. I think the tube was getting hung up on the curved part. |
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I've been following your threads on this problem and looking forward to what you figure out. I just finished a build where my ejected brass has been hitting the edge/corner of the ejection port and not where I want it to hit (in the middle of the shell deflector), so I'm going to observe on the next outing where it is hitting and have an H buffer to put in vs a standard carbine, and also have a BCM extractor spring kit if that'd do the trick. I know there is nothing functionally wrong with the rifle because it cycles fine and locks on last round just fine. But I'm still going to do what I can to get the ejection off of where it is so it can stop chipping away at the upper receiver, if possible.
My rifle specs are DD phosphate BCG, DD 16" midlength barrel, DD Low profile gas block pinned, raptor CH, and the upper is a Mega Billet. PSA buffer tube and spring with their standard buffer at the moment. And my bolt, when locked back, does stick forward where you can see it through the ejection port like 1/4", unlike the issue you are experiencing where it is clearly too far back. |
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I've been following your threads on this problem and looking forward to what you figure out. I just finished a build where my ejected brass has been hitting the edge/corner of the ejection port and not where I want it to hit (in the middle of the shell deflector), so I'm going to observe on the next outing where it is hitting and have an H buffer to put in vs a standard carbine, and also have a BCM extractor spring kit if that'd do the trick. I know there is nothing functionally wrong with the rifle because it cycles fine and locks on last round just fine. But I'm still going to do what I can to get the ejection off of where it is so it can stop chipping away at the upper receiver, if possible. My rifle specs are DD phosphate BCG, DD 16" midlength barrel, DD Low profile gas block pinned, raptor CH, and the upper is a Mega Billet. PSA buffer tube and spring with their standard buffer at the moment. And my bolt, when locked back, does stick forward where you can see it through the ejection port like 1/4", unlike the issue you are experiencing where it is clearly too far back. Maybe check your PSA tube. That's where I got mine. And I'm guessing it's a bit long and it needed to be addressed. I think just a shoddy finishing job. You can see in the pic where it looks wonky. The bottom part is actually in the top of the pic, where the retainer pin would be going: 
(I guess there's a reason they are only like 40 bucks for the whole assembly. But it's supposed to be the right type of metal.......) So I busted out the file and relieved it. I only needed a hair. Maybe a 1/32". 
Boom. Done. 
Now I need to borrow my buddies AR tool and snug it down. Smack it for staking and I keep on debating on if I want to paint this carbine. OD. I'm not convinced I do though...... Actually, I've been kind of a filing fool lately. I filed down the CAR stock because the little wings at the mouth or front bug the living crap out of me. So I made it a bit smoother and now I like that stock again, without the rubber buttpad. 
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The buffer tube I got from PSA definitely didn't look like that. I got mine from PSA in a rifle build kit because from everything I was told they use 7075 aluminum vs 6061. There's clearly no way to tell the difference so I wouldn't even know if I had received a 6061 one. But I read somewhere before purchasing that they only make 7075 buffer tubes.
Here are some pics of mine installed. And what I am talking about for where it is hitting/chipping the anodizing. Obviously it isn't terrible, but if it continuously hits there it will get worse, and I think I can prevent it. I read many threads saying "oh its fine don't worry about it", which I don't disagree that functionally it is working fine. However, I would like it to not do that, and I believe that I can remedy it by changing a couple of things on the rifle. Whether it be the BCM H buffer I bought or the BCM extractor spring upgrade kit. I know my dad's rifle running almost the exact same components (DD 16" midlength barrel, DD pinned low profile gas block, carbine buffer, BCM BCG, BCM buffer spring and buffer tube) does not have extractions hitting where mine is hitting. 
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This is where the receiver extension is supposed to rest - rifle receiver extension shown, which indexes to the lip on the tube, not any particular number of rotations.
If your carbine receiver extension varies from this, something's slightly out of spec, and one of the solutions as shown by JJREA above is to leave a lip that can be easily modified by the user without having to face the entire tube to get the correct depth and correct overlap of the buffer retainer pin. 
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The buffer tube I got from PSA definitely didn't look like that. I got mine from PSA in a rifle build kit because from everything I was told they use 7075 aluminum vs 6061. There's clearly no way to tell the difference so I wouldn't even know if I had received a 6061 one. But I read somewhere before purchasing that they only make 7075 buffer tubes. Here are some pics of mine installed. And what I am talking about for where it is hitting/chipping the anodizing. Obviously it isn't terrible, but if it continuously hits there it will get worse, and I think I can prevent it. I read many threads saying "oh its fine don't worry about it", which I don't disagree that functionally it is working fine. However, I would like it to not do that, and I believe that I can remedy it by changing a couple of things on the rifle. Whether it be the BCM H buffer I bought or the BCM extractor spring upgrade kit. I know my dad's rifle running almost the exact same components (DD 16" midlength barrel, DD pinned low profile gas block, carbine buffer, BCM BCG, BCM buffer spring and buffer tube) does not have extractions hitting where mine is hitting. <a href="http://s1209.photobucket.com/user/WS6Dream/media/IMAG1259_zpszcifwl8j.jpg.html" target="_blank">http://i1209.photobucket.com/albums/cc382/WS6Dream/IMAG1259_zpszcifwl8j.jpg</a> <a href="http://s1209.photobucket.com/user/WS6Dream/media/IMAG1260_zpsjofmqarm.jpg.html" target="_blank">http://i1209.photobucket.com/albums/cc382/WS6Dream/IMAG1260_zpsjofmqarm.jpg</a> <a href="http://s1209.photobucket.com/user/WS6Dream/media/IMAG1261_zpsequ0vcjg.jpg.html" target="_blank">http://i1209.photobucket.com/albums/cc382/WS6Dream/IMAG1261_zpsequ0vcjg.jpg</a> Yeah, I'm not sure what to tell you. I think your tube looks like it's in their the right amount, according to the other photos shown. And mine seems to be now too. The brunton bump is going to get beat up to some extent, it's meant to deflect the brass. Yours definitely seems like it focusing on that one little spot. It almost looks like your bump is concave, and that's not how a typical upper is. Which might be contributing? I don't know. I can see why you might not want it to muck up that fancy finish. For me, I just want to make sure it was done proper. It looks like my buffer tube was too long and it was out one thread too far before I fixed it. But yeah, the PSA tubes are supposed to be the "right" kind of materal.  And a really good price. The little that I did to it, I'm not complaining. I just didn't really know any better.
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My experiment years ago showed that both these levels of contact worked fine. 20" rifle I installed a carbine tube on.
 BuffRetainIn by FredMan, on Flickr
 BuffRetainOut by FredMan, on Flickr
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My experiment years ago showed that both these levels of contact worked fine. 20" rifle I installed a carbine tube on. <a href="https://flic.kr/p/FrJzqG" target="_blank">https://farm2.staticflickr.com/1611/25889133500_11830d0e10_z.jpg</a>BuffRetainIn by FredMan, on Flickr <a href="https://flic.kr/p/EWpzrQ" target="_blank">https://farm2.staticflickr.com/1544/25557248054_e59694376f_z.jpg</a>BuffRetainOut by FredMan, on Flickr Hey Fred, Do you have the ability to pair that lower with a suspected over gassed carbine URG and run the experiment again? Checking to see if the change in OAL from barrel extension to the bottom of the receiver extension will effect ejection patterns? The change in length causing the bolt face to stop at different points in relation to the ejection port and shell deflector. I would love to see a write up on this with say Molons attention to detail. I'm by far no engineer. |
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Below are a couple of threads concerning receiver extension and bolt face orientation.
AR15.com trouble shooting Another |
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Below are a couple of threads concerning receiver extension and bolt face orientation. AR15.com trouble shooting Another Thank you sir. That pretty much sums it up. |
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In my experience, PSA gets receiver extensions from more than one supplier, which means, even if they are all "MIL SPEC," they may not all be made identically.
As shown in various pictures, you need to have sufficient coverage of the back of the buffer retainer to keep it in place. If it isn't held down well enough, the tip of the retainer can rub on the groove in the bolt carrier tail, which can cause all sorts of problems. |
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CD said the military spec is just that the tube holds the pin in. Nothing about indexing the bolt to the port. Interesting. He said he's had them long he's had them short. As long as it keeps the pin in, then it's good to go. It's in the Block II thread if anyone wants to read it. I suppose I should quote it here:
"per Techincal Manual TM 9-1005-319-23&P page 0025-8 10. Push down on buffer retainer (11) and helical spring (12) and, at the same time, screw lower receiver extension (8) in until it retains buffer retainer in position. CD" Soooooooo, I'm assuming that means you don't typically check where the bolt ends up when you pull back on the CH? Just as long as the pin is retained? Do you see variances in tube lengths that would change the position of the tube from time to time? "Correct, actually never check the position of the bolt. If parts are built to mil spec length should be there. Would only check is something isn't funcutioning properly. I've had receiver extensions go where yours is or all the way forward. Both are correct, pin need to be retained. Cartridges still eject fine in both positions in my experience. CD" |
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As long as the bolt goes back far enough for the bolt catch to work, I don't care how much farther back it goes. But the real issue is that your receiver extension must hold the buffer retainer well enough that it doesn't interfere with operation of the carrier.
Some receiver extensions have a "lip" on the bottom, which extends forward and holds down the buffer retainer. Others are just threaded all the way to the end. Whatever works for you and the stock you chose for the gun (as long as it retains the buffer retainer and it's straight!) is the "right way" to install a receiver extension. |
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CD said the military spec is just that the tube holds the pin in. Nothing about indexing the bolt to the port. Interesting. He said he's had them long he's had them short. As long as it keeps the pin in, then it's good to go. It's in the Block II thread if anyone wants to read it. I suppose I should quote it here: "per Techincal Manual TM 9-1005-319-23&P page 0025-8 10. Push down on buffer retainer (11) and helical spring (12) and, at the same time, screw lower receiver extension (8) in until it retains buffer retainer in position. CD" Soooooooo, I'm assuming that means you don't typically check where the bolt ends up when you pull back on the CH? Just as long as the pin is retained? Do you see variances in tube lengths that would change the position of the tube from time to time? "Correct, actually never check the position of the bolt. If parts are built to mil spec length should be there. Would only check is something isn't funcutioning properly. I've had receiver extensions go where yours is or all the way forward. Both are correct, pin need to be retained. Cartridges still eject fine in both positions in my experience. CD" The following is based on personal learning alone, I am not an expert. I'm in the group that does check how far back the bolt goes and I use a spacer if needed to make sure the bolt is visible about 1/8 inch in the port. The nicely shooting factory rifles I have checked all seem to have this. I do not have any of the photos to show bolt and receiver relationship, but it is possible for the BCG to go back far enough in some situations so that the BCG hits the lower receiver in the rear. Honestly, I'm not sure that it matters in the lifespan of our shooting these rifles but it's and easy thing to do. It also helps the timing of brass ejection. I think when there were few manufacturers of "mil spec" parts , i.e. Colt, the receiver tubes were maybe closer to the same. Now days, mil spec seems to mean diameter only , so caveat emptor on the length of the tube you will get. It is also a very controversial area so YMMV. |
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The BCG should be visible in the port about 1/8 ", if it retracts too far you can put a spacer, like a quarter,in the tube before the buffer spring goes in. If the rear position of the bolt is the big concern, this is all you need to do. Some people use quarters, but washers, etc. also work. Drop something into the bottom of the tube before installing buffer and spring, so that they don't travel as deep into the tube and call it a day. Especially if you've already staked the castle nut. I can't imagine trying to re-do that without replacing the sling/latch plate. FWIW: I have always used the bolt catch as the reference point for how far back the bolt should travel, not the ejection port. |
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here a few photos of one of mine. So to explain. The buffer retaining plug has a little forward backward movement in the hole. It sits flush when the buffer is out but once the buffer contacts the pin it shifts forward a tad. This is a Spikes lower with Spikes buffer tube assembly. There doesn't seem to be any functional issues and I have already staked my castle nut so I see no reason to take it apart at this point?
First photo shows how the plug is aligned when i nudge it to the back of the hole. 
This photo shows how it is when the movement pushes it towards the front of the hold 
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