View Full Version : Mating of Buffer Tube w/ Retaining Pin Help
Hey guys,
First of all, Happy Veteran's Day to all the vets on here.
Here is a pic of my buffer tube/retaining pin. The tube has caught the retaining pin, but is it good enough?
I already torqued and staked the castle nut, but . . .
Edit: I added some better pictures across all three current builds. You should be able to better see which one I am concerned with. Also, the lowers are Aero and the tubes are all Larue.
Renegade04
11-11-17, 18:44
It is barely contacting the buffer detent. I would not trust it. The buffer tube is usually almost all the way up to the base of the tip of the detent. Yours is barely on the detent itself.
GeneralPurpose
11-11-17, 18:52
That's extremely minimal engagement. Can you turn the buffer tube another full rotation, or does it hit the tip of the detent first? If you can get another rotation, I'd do it. If not...I'm not really sure what your options are other than to try a different tube.
That's extremely minimal engagement. Can you turn the buffer tube another full rotation, or does it hit the tip of the detent first? If you can get another rotation, I'd do it. If not...I'm not really sure what your options are other than to try a different tube.
Naw, I can't turn it another full rotation. I thought everything looked good before I staked it too. I need a light on my workbench.
Is it normal for buffer tubes to not take to certain receivers? My other tubes and receivers (from the same respective manufacturers) mated up nice and tight.
It looks like the tube is jammed up against the retaining pin, instead of the pin being under the tube. It probably would have been fine if you would have held the pin down enough when screwing the tube in.
It looks like the tube is jammed up against the retaining pin, instead of the pin being under the tube. It probably would have been fine if you would have held the pin down enough when screwing the tube in.
I'll double check, but I am pretty sure it is under the tube.
It looks like the tube is jammed up against the retaining pin, instead of the pin being under the tube. It probably would have been fine if you would have held the pin down enough when screwing the tube in.
This is exactly what I thought.
This is exactly what I thought.
I checked, the retainer is under the tube -just a bit.
You should be able to get another full turn on the RE. Be sure to push down on the retainer when you do. Unfortunately, you'll need to break the staking which isn't hard, but your end plate will be left kinda ugly. Either replace the end plate or use some cold blue or paint, or don't.
You really don't want the retainer to pop out during firing.
GeneralPurpose
11-11-17, 20:54
Naw, I can't turn it another full rotation. I thought everything looked good before I staked it too. I need a light on my workbench.
Is it normal for buffer tubes to not take to certain receivers? My other tubes and receivers (from the same respective manufacturers) mated up nice and tight.
It happens from time to time. My buddy absolutely could not get his receiver to work with a LaRue buffer tube. I checked it for him and it was just perfectly (imperfectly?) between rotations. One rotation out wouldn't engage, one rotation in would hit the pin. I don't think it's very common but it can happen based on the thread pitch vs. the dimension between the edge of the retaining pin and the post. Really annoying but at least buffer tubes don't cost too much money.
bamashooter
11-11-17, 21:07
The tube appears under the pin to me.
Does the pin push down freely to release the buffer? It must be an illusion on that picture because it doesn’t look like the pin is under the tube. I’ve had some tubes that just barely catch the edge of the retaining pin. As long as the retaining pin is under the tube, even barely, it should be fine. The buffer should never touch the pin after you close the receivers.
GeneralPurpose
11-11-17, 21:32
For those saying it looks likes the pin is under the tube...look at the 1:00 position. The tube has a little bit that's offset and overlaps the pin. It barely overlaps it, but it's there.
For those saying it looks likes the pin is under the tube...look at the 1:00 position. The tube has a little bit that's offset and overlaps the pin. It barely overlaps it, but it's there.
I see that and the rest of the pin looks like it’s on top of the tube, that’s why I asked if the pin pushes down freely.
GeneralPurpose
11-11-17, 21:49
I see that and the rest of the pin looks like it’s on top of the tube, that’s why I asked if the pin pushes down freely.
It's the M.C. Escher of buffer tubes. :)
Yeah the pin pushes down freely, only resistance is the spring. I doubled checked, and it is under the tube.
It is odd because my other lowers all use Aero receivers and Larue tubes, but this is the only tube that doesn't overlap the retainer quite a bit -nearly butts up to the little "pin" on top of the retainer. I will take another photo for a point of comparison in the morning.
Literally trying to get the buffer tube perfectly aligned was the most challenging parts of the build so far -not the bolt catch haha. Tubes wanted to rotate when torquing the castle nut.
Just don't know if I trust it as is....
GeneralPurpose
11-11-17, 22:25
I wouldn't trust it as is. That looks like it'll pop up under recoil.
Yeah, Larue products seem to have their own quirks in my experience.
I will try and back off the nut without ruining the qd plate. Otherwise I'll just order another from Earl over at Impact Weapon Compenents. I'll let you guys know how it goes.
Yeh that can be tough. Most of the time I have to do it a couple of times before I get a torqued castle nut on a straight, indexed tube. This can be a PITA when you have OCD. I would like to see another picture of yours, it doesn’t look right.
Just don't know if I trust it as is....
You really don't have to trust it, unless you want to. The rifle/carbine will function just fine without the retainer. Just have to hold the buffer back with your finger until you get the upper partially closed.
I wouldn't shoot it with the retainer barely held in place like that, you do not want it popping loose and risk getting the spring and the retainer in your action while firing.
So you either need to fix it or remove it.
I noticed your receiver extension has a partial lip on it, like these do, you can see it in your picture:
4858148582
What I would do is disassemble, and then reassemble w/o the retainer, stop at the edge of the 'hole' and then rotate one more turn, see if filing off that lip would give you a proper fit. I ass-u-me that is what the lip is for.
Or, you could by an offset retainer pin from this guy: http://commonbullets.com/wp/archives/1727
Good luck. whatever you decide.
ETA: your buffer tube/receiver extension shouldn't be turning much at all, their is a machined groove at the bottom of the tube/extension which corresponds with the tang on the end plate to stop rotation.
As said, looks like the tube has a notch around the pin.
Probably not “right”, but I had one like that Ian’s I sanded down the tube to allow another rotation. Never had an issue with it. Or you could buy a new tube.
Without knowing more about the components, the fault is either with the lower, the extension or both. We had to reject a few hundred extensions over the last 2 years or so as they were not made correctly and created the exact issue you are now having.
I have also seen lowers where the hole was milled wrong.
Without knowing more about the components, the fault is either with the lower, the extension or both. We had to reject a few hundred extensions over the last 2 years or so as they were not made correctly and created the exact issue you are now having.
I have also seen lowers where the hole was milled wrong.
What should I check for when I get a new lower/buffer tube? Also, I updated the first post to show better pictures across my three builds. All the same lowers (aero) and buffer tube (larue)
I think that RE tube just needs another turn in.
bamashooter
11-12-17, 12:45
I made a "false" stereo pair from the OP's original image. It'll work for this thread. You be the judge.
For anyone inexperienced at this, while viewing the image, lightly begin crossing your eyes until the "pair" lock together as a single, 3D image (middle image).
https://i.imgur.com/NF3wkPd.jpg
I guess I don't understand why the stereo image is useful -although I appreciate your help.
I've been looking up pictures of buffer tubes and it seems like most have a straight edge, idk why this one has the notch for the retainer -style?
bamashooter
11-12-17, 13:21
Perhaps larger will help but a tad pixelated.
https://i.imgur.com/5YLdWkD.jpg
Perhaps larger will help but a tad pixelated.
https://i.imgur.com/5YLdWkD.jpg
I don’t get it. Honestly, it looks like the detent was punched through the tube.
Looks like that notch is common to the Larue tubes as evidenced by the OP's pictures and this one from Larue's site. Maybe they mis-timed the threads and did the notch to save them. There is no notch on my BCM and Vltor tubes. It looks like it will screw in another thread if you depress the pin completely to allow the small post (not just the body) to clear until it reaches the notch. Picture from Larue site>>
https://i.imgur.com/j2LUDY6.jpg
bamashooter
11-12-17, 14:42
Ok, See the deal. Bronchitis is messing with my head. Some tubes have notches, some don't. Here's my notched tube against the "stem" of the retainer pin. Your's is not making it to the stem which I assume is not by design. If you depress the pin will the tube screw in that small additional amount?
https://i.imgur.com/5uW0RTl.jpg
https://i.imgur.com/UQXnZhH.jpg
Internet photo on bottom (3rd)
https://i.imgur.com/I787HDr.jpg
My LaRue tube has the 'lip' but no notch, mine times perfectly with the detent pin.
So, either take the lip off, as I suggested earlier, or make the notch bigger, which wouls seem to be easier.
It's not that easy. It kind of comes with years of experience and seeing all kinds of parts (good and bad). When I install an extension onto a lower I am looking for engagement that is approx. 1/2 the distance from the edge of the pin to the center post.
What should I check for when I get a new lower/buffer tube? Also, I updated the first post to show better pictures across my three builds. All the same lowers (aero) and buffer tube (larue)
You may be right, but it looks to me that if you turn it one more time, it will not time right, or the top of the extension will protrude past the lower receiver's threaded area.
I think that RE tube just needs another turn in.
It's not that easy. It kind of comes with years of experience and seeing all kinds of parts (good and bad). When I install an extension onto a lower I am looking for engagement that is approx. 1/2 the distance from the edge of the pin to the center post.
Now right there ^ is very useful information! I think if the notch wasn’t in that tube it would be very close to that. That’s why I don’t build my own serious business guns. By the time you buy parts and run into crap that ultimately cost more, why not buy a complete lower from a reputable manufacturer? People think these things are easy because some people make it look easy.
Hey guys,
So I spent today studying for an exam and working on this lower.
Regarding the buffer tube, I took it apart -it was a little difficult but the staking I had previously done, didn't make it impossible. I found that a couple of the thread teeth (you can see in the second picture) took some damage. Idk if this is normal or not.
I took it all apart, re-greased it and gave it an extra twist. The tube seems to cover up the retainer better, but just barely sticks into the receiver.
However, when I started to put the torque on the castle nut I ran into issues. Now this got interesting because "the tube" started to twist counter-clockwise when I was torquing the castle nut. It started to deform just to the left of the notch cut into the tube. You can see this as the shiny part to the left.
Now, I went to talk to my dad because he is a mechanic. He told me that the receiver is twisting in the same direction of the applied torque, but because the buffer tube is being captured by the vise (actually the Geissele Reaction Block) it appears that the tube is moving. So I took it all apart again and went to re-torque the castle nut and sure enough he was right -the lower was trying to twist and (like my Dad suggested) I just held the lower tightly and it went smoothly this time.
So, I don't know why this became such a hassle as I have worked around torque wrenches and tools through cars, but I am new to building ARs. Should I be worried about the stripped areas of the threads? Or that the buffer tube does, ever so slightly, poke into the receiver. I really mean, barely.
Once again, I appreciate everyone's help. It's frustrating because I know what to do intellectually, but I don't have the experience I guess. I can see why people buy factory rifles, but eventually I'll be building rifles just as well -I just need that experience I don't have.
bamashooter
11-12-17, 19:32
The knowledgeable folks will be here soon enough. But I know this. Never, ever give up young man. You'll be just fine.
The knowledgeable folks will be here soon enough. But I know this. Never, ever give up young man. You'll be just fine.
Looks like this one is going south.
bamashooter
11-12-17, 21:51
Likely. As they say, one of those "teaching moments".
The retainer engagement looks much better, but the tube is poking out and you may have issues closing the upper.
The retainer engagement looks much better, but the tube is poking out and you may have issues closing the upper.
I tested up the upper/lower fit and it is tight, but I can close it. The takedown pins + cerakote is another story haha. Tight is an understatement.
I still don't understand why the threads on the buffer tube broke.
You mean the shiny spots on either side of the keyway? That's caused by inadvertent rotation either during install or removal. Check the depth of the end plate key (the tab that runs in that track). I'm thinking that there might be a small gap between it and the tube. If there is, its less to keep the RE from turning so the threads pay the price. I'm just speculating here since I didn't see or do the fitting and install myself.
I still don't understand why the threads on the buffer tube broke.
Yeah I figured it had something to do with the end plate. Tube still threaded in nice and smooth -I also greased it a lot -so I am just going to use it as I didn't see a flood of "NO! Don't use it" responses.
It's frustrating as I said before because I don't have the experience to diagnose these issues, or even know how to learn from these issues and grow. I have build ARs with local gunsmiths and never ran into these issues -then again it's my first time using the G Reaction Block too.
I'm just trying to learn and get better each time. I really like building them, but this whole process has also made me feel real dumb for even trying to become an AR builder.
As long as your stock stays put it should be fine.
Don't give up. Keep building. Only hands-on experience will suffice.
Cool. I was on the fence about getting a new buffer tube, but decided to keep the one with the broken threads. It threaded fine and everything seems to be good.
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