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Basic
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Posted: 6/24/2012 7:35:21 AM EST
Shooting an Alex Arms Upper in 6.5 Grendel
and a Bushmaster Lower. After about 5 rounds- all of which feed fine, the BCA jams. After opening the rifle the Buffer retainer pin and its spring are found under the bolt. The buffer retainer spring is destroyed.

So I obtained a new Wolf Buffer spring, new retainer pin and spring, new buffer, and new bufffer tube from Brownells.
I tested the rifle and cycled the Bolt several times, and there was no problem. The Buffer retainer pin held its position under the edge of the Buffer tube which was thoroughly screwed in tight.

So at the range today, the same thing happened after about 5 rounds. The buffer retainer pin popped out, the buffer pin retainer spring was jammed under the BCA.
My loads are really not hot. Using Lapua Brass, 27.2 Gr of VV N140 and 123 gr 6.5mm Laupa bullet, and CCI primers.

What is with the Buffer system and how do I fix it? hve gone through 2 sets of parts...Is it the BCA?

Thanks. I know there is an expert here who can help out.
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Link Posted: 6/24/2012 9:57:03 AM EST
maybe your bcg is hitting the pin...

is the channel in the bottom of it machined all the way?

maybe your bcg has too much rearward travel?
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Link Posted: 6/24/2012 10:32:14 AM EST
Can you take a picture of the buffer tube and retaining pin?
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Link Posted: 6/24/2012 11:14:00 AM EST
Originally Posted By Obo2:
maybe your bcg is hitting the pin...

is the channel in the bottom of it machined all the way?

maybe your bcg has too much rearward travel?

This ^^^
Sounds like your carrier is hitting the retainer pin.
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Link Posted: 6/24/2012 11:51:22 AM EST
[Last Edit: 6/24/2012 3:54:40 PM EST by Dano523]
Posted By PlaymoreMinds:

'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...

<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Link Posted: 6/24/2012 11:54:19 AM EST
Checked the bolt carrier and the channel is smooth and cleanly cut
The upper closes on the lower assembly and as is shuld slightly pushes the buffer back so it does not rest on the buffer retaining pin.
I have tried two buffer retainer pins one old and the other from Brownells that I put in this week.
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Link Posted: 6/24/2012 1:01:45 PM EST
If the pin is coming out then the tube isn't far enough in.

It should look like this:

Photo by stickman


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Link Posted: 6/24/2012 2:15:31 PM EST
Got new tube this wk
It is screwed all the way in, It holds the retainer pin in place with the receiver open.
Checked the bolt carrier and there is no defect in the slot that rides over the buffer retainer pin. Cloxint the assembly demonstrates the buffer is pushed back enough that it does not hit the retainer pin.
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Link Posted: 6/24/2012 4:53:37 PM EST
[Last Edit: 6/24/2012 4:55:14 PM EST by Direct-Drive]
Originally Posted By fx77:
Got new tube this wk
It is screwed all the way in, It holds the retainer pin in place with the receiver open.
Checked the bolt carrier and there is no defect in the slot that rides over the buffer retainer pin. Cloxint the assembly demonstrates the buffer is pushed back enough that it does not hit the retainer pin.

If you're in the right spot, one additional (attempted) rev would cause the tube to bind on the pin which is undesirable, of course.

There must have been tube damage or receiver damage for that retainer to escape ?
Something's hitting it and the buffer is being properly held back, so it has to be part of the carrier making contact.

What if you took some White-Out and painted the pin, then cycled the weapon by hand.
Inspect the pin.
Also observe how much "bolt is showing" at the back of the ejection port when fully retracted by hand.
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Link Posted: 6/25/2012 3:42:55 AM EST
Great idea with Wite Out
PAinted the pin. Retracted the bold manually and inspected the underside of the BCA and noted the slot in the underside cleared the pin . There was no resistance.
When the bolt is retracted it is full y in the right place.
My inspection of the buffer pin and tube are just like the posted picture above.
Now what?
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Link Posted: 6/25/2012 7:25:58 AM EST
[Last Edit: 6/25/2012 7:26:31 AM EST by Direct-Drive]
Originally Posted By fx77:
Great idea with Wite Out
PAinted the pin. Retracted the bold manually and inspected the underside of the BCA and noted the slot in the underside cleared the pin . There was no resistance.

So the White-Out remained intact.....no rub marks with the BCG fully retracted to its farthest point ?

When the bolt is retracted it is full y in the right place.

Does the bolt disappear to the rear of the ejection port when being held back as far as it will travel ?

My inspection of the buffer pin and tube are just like the posted picture above.
Now what?

I'm still wondering how the retainer is escaping if the tube is threaded in to the correct distance.

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Link Posted: 6/25/2012 8:09:27 AM EST
Bolt appears all the way back when fully retracted.
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Link Posted: 6/25/2012 8:38:39 AM EST
Originally Posted By fx77:
Bolt appears all the way back when fully retracted.

So the bolt is not visible in the ejection port when the BCG is fully retracted 100% of the way back ?

If yes, one of the posters above eluded to reducing the rearward travel of the bolt.
The theory is that maybe the forward section of the carrier is making contact with the retainer pin.
You can show approx 1/8" - 3/16" of bolt in the ejection port and still have enough rearward travel for the bolt catch to work.
To do this you have to spacer the buffer tube. You can use washers, quarters, what have you, to get the desired spacing.
The spacers are placed under the rear end of the spring, then reinstall the spring/buffer system.

Is it possible that this whole scenario was originally caused by the buffer tube not being threaded in the correct distance ?
I can't see how the retainer and spring could have escaped without tube or receiver damage.


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Link Posted: 6/25/2012 9:09:25 AM EST
if you don't want to use spacers you can lap down the RE so that it screws in further.

check your lower receiver to be certain it is not cracked or damaged allowing the pin to escape.
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Link Posted: 6/25/2012 11:39:16 AM EST
Very good advice so far Thanks.
My eyes ain't what they used to be..neither is anything else, but another time

Under 3.5 X loupe magnification I note the hole in which the buffer ret. pin sits is not round. it is ovoid in the front and round in the back ..maybe from the pin slamming the front when the buffer retainer or the bolt catches it on the forward return?
Anyway than might explain how it could be levered out of its socket. May have to build another lower with a better buffer retainer pin hole

What do you think?
Hard to tell which came forst at this point in time..a bad hole in the lower or damage from the buffer retaining pin being levered out on the return of the bolt to battery.
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Link Posted: 6/25/2012 2:12:04 PM EST
[Last Edit: 6/25/2012 2:17:56 PM EST by Dano523]
Posted By PlaymoreMinds:

'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...

<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Link Posted: 6/25/2012 2:16:39 PM EST
please post pics of your lower
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Link Posted: 6/25/2012 4:41:28 PM EST
[Last Edit: 6/25/2012 6:41:37 PM EST by Dano523]
Pic Requested of Buffer pin and Lower buffert ube relationship

http://img545.imageshack.us/img545/7990/bufferpinwithwiteout.jpg
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Link Posted: 6/25/2012 4:43:26 PM EST
Cut the sucker!
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Link Posted: 6/25/2012 5:19:36 PM EST
[Last Edit: 6/25/2012 5:20:40 PM EST by glgtwenty]
I don't want to speak for any of the guys that have been helping you out, but in case they are gone for the night, here's my take on that picture.

It sure looks to me like the buffer tube is not screwed in far enough.

It looks like the buffer itself is the only thing holding that buffer retaining pin in as it sits.
You should be able to see the end of the buffer tube in that picture with the buffer inside it... not sticking way out past the end like that.

you have to push that buffer retaining pin down and continue to screw that buffer tube in another turn or so... so that is is sitting on the lower shoulder portion of the retaining pin, just like the buffer itself is now in your picture.

sorry if i'm not lokign at it right. :)


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Link Posted: 6/25/2012 6:42:41 PM EST
[Last Edit: 6/25/2012 6:52:30 PM EST by Direct-Drive]
Originally Posted By glgtwenty:
I don't want to speak for any of the guys that have been helping you out, but in case they are gone for the night, here's my take on that picture.

It sure looks to me like the buffer tube is not screwed in far enough.

It looks like the buffer itself is the only thing holding that buffer retaining pin in as it sits.
You should be able to see the end of the buffer tube in that picture with the buffer inside it... not sticking way out past the end like that.

you have to push that buffer retaining pin down and continue to screw that buffer tube in another turn or so... so that is is sitting on the lower shoulder portion of the retaining pin, just like the buffer itself is now in your picture.

sorry if i'm not lokign at it right. :)



agree with glg.

It looks like if you were to push back that buffer the retainer and spring would come flying out.
Thankfully the forward edge of the retainer bore still looks good. I've seen these broken out.

Please remove the buffer and spring and show us the tube/pin relationship.

Edit:
I also see that your White-Out has been scraped off the top of the pin.
This may be from contact with the carrier.




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Link Posted: 6/25/2012 6:44:42 PM EST
Posted By PlaymoreMinds:

'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...

<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Link Posted: 6/26/2012 2:25:15 AM EST
Ok but now I have invested in a second buffer tube and honestly it is screwed in as far as it can go. That means "?" lapping the buffer lower junction to get it to screw further inward to push on the buffer pin?
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Link Posted: 6/26/2012 2:26:28 AM EST
Oh yeah an dlae today maybe I can get a picture up with the buffer removed and demonstrate the tube pin relationship.
Cut the sucker!
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Link Posted: 6/26/2012 2:51:40 AM EST

Originally Posted By fx77:
Ok but now I have invested in a second buffer tube and honestly it is screwed in as far as it can go. That means "?" lapping the buffer lower junction to get it to screw further inward to push on the buffer pin?

try and put up a picture showing more of the back end of that lower where the buffer tube threads in.
if you took out the buffer, buffer spring, buffer retaining pin and buffer retaining pin spring, you should be able to screw that buffer tube in until it covers or least nearly covers that buffer retaining pin hole.
the buffer tube is not threaded enough, has damaged threads or the lower has too much metal in the buffer tube hole area making the buffer tube socket too deep (too many threads). that would be where you said lap it , but it sounds and looks like more than my definition of lapping... like cutting off a sliver and then filing/sanding down the edge.

I think we're on the same page anyway, but as for what to lap or file or grind off... better leave that for the other guys above that seem to know.
I can only say that it ain't fitting together right!
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Link Posted: 6/26/2012 3:55:44 AM EST
Posted By PlaymoreMinds:

'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...

<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Link Posted: 6/26/2012 6:10:35 AM EST
Originally Posted By fx77:
Ok but now I have invested in a second buffer tube and honestly it is screwed in as far as it can go. That means "?" lapping the buffer lower junction to get it to screw further inward to push on the buffer pin?

I'm going to go out on a limb and say from your pic that you are not differentiating between the retainer body and the retainer pin.
It looks you are trying to bump the retainer body with the tube and not the actual pin.
If that's correct, then that's the root of all your troubles.

You must come in over the top of the retainer body with the tube and get as close to the pin as you can without binding it.
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Link Posted: 6/26/2012 9:15:11 AM EST
Here is a pic of the lower with the buffer tube screwed all in
The buffer retainer pin and spring removed.

http://img217.imageshack.us/img217/8373/004sfu.jpg
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Link Posted: 6/26/2012 9:15:58 AM EST
http://imageshack.us/photo/my-images/217/004sfu.jpg/
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Link Posted: 6/26/2012 9:17:06 AM EST
URL=http://imageshack.us/photo/my-images/217/004sfu.jpg/]http://img217.imageshack.us/img217/8373/004sfu.jpg[/URL]
Cut the sucker!
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Link Posted: 6/26/2012 10:04:51 AM EST
yeah if that's all the way in, then I think it's not going in quite far enough. coupled with the oval or elongated hole you mentioned up above, it sure looks like the pin may be able to slip by the end of that tube. espeicaly if it just takes a little notch out of the end of the tube on it's way to popping out.

It's hard to say for sure tha't snot far enough, but in my experience, the buffer tube is able to screw in and cover the hole..... so you find the sweet spot and tighten down the locking ring.

So, if that picture is "all the way in" then I'd say your question is now, what's stopping the buffer tube from going in far enough?


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Link Posted: 6/26/2012 11:29:40 AM EST
Buffer tube stops when the shoulder of the tube hits the lower.
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Link Posted: 6/26/2012 11:47:33 AM EST

Originally Posted By fx77:
Buffer tube stops when the shoulder of the tube hits the lower.

yeah someone else will have to address that, I'm only familiar with buffer tubes that are the same size and threaded back a couple inches. Then there is a... basically a jam nut they call the locking ring that lets you tighten it down against the lower receiver when you have the buffer tube screwed in to your desired position.

I can't speak to a buffer tube with fixed shoulder on it that contacts the lower reciever. (With what i'm talking about above the locking ring provides that shoulder, but the locking ring is threaded and can be spun forward or back on the buffer tube )
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Link Posted: 6/26/2012 1:49:31 PM EST
[Last Edit: 6/26/2012 2:09:38 PM EST by Direct-Drive]
Originally Posted By fx77:
Buffer tube stops when the shoulder of the tube hits the lower.

Up until now we didn't know that you are working with a rifle tube.
I thought that this was a carbine tube.

You have something out of spec and it's probably the lower because apparently two different buffer tubes have yielded the same result.
That's not enough coverage over the retainer.

The grapevine says that CS from Bushmaster is lacking, but you could try contacting them anyway and see what they say.
Or you could go to a carbine buttstock system that will allow you to manipulate the distance that the tube penetrates the receiver.
The carbine tube does not have a stop on it like your rifle tube. It uses a castle nut for the stop.

One other option is to run without a buffer retainer but you have to deal with the buffer and spring each time you open the receivers for cleaning.
I suppose you could make up a dowel to serve as a temporary retainer while the receivers are open.
It would be workable, but not ideal to be sure.
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Link Posted: 6/27/2012 2:26:41 AM EST
Posted By PlaymoreMinds:

'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...

<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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