buffer 'chatter' marks, what causes it?

Jayne

Jayne

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I saw in a video the idea of buffer 'chatter' where it bangs into the buffer retaining pin all the time. I looked at my primary AR and sure enough it's showing signs:

IMG_2960.JPG

All the way around it's marked up from hitting the retaining pin. This lower has ~7k rounds through it.

Should I be concerned? What's the failure mode for that pin? At some point I open the rifle to clean it and the buffer spring assembly flies out?

Is there a fix besides replacing the lower?
 
From what I have read the only real failure point is if the little nub breaks off and falls into your fcg.

If your worried about it just remove the retaining pin.

Just know that it will be like those snake in a can gags every time you separate the receivers. Don't want that buffer knocking someone's tooth out.
 
If the buffer retainer spring breaks off, it can jam up the rifle depending on where it gets lodged.

The Buffer isn't suppose to rest on the pin with the gun is closed, so something is slightly out of spec. Could be the pin location or the BCG.
 
I'd expect the aluminum lower to elongate the retaining pin hole before the pin to break.
 
Timfoilhat said:
I'd expect the aluminum lower to elongate the retaining pin hole before the pin to break.
Click to expand...
My experience has been the opposite. I would begin looking into what is causing it to hit the retaining pin while the receivers are closed.
 
Out of curiosity, is this a lower that has one of those tension screws under the pistol grip to tighten up slop between the upper and lower?
 
Interesting. Caused me to research it a little. Multiple schools of thought and YMMV.

1. Do you use a .22 conversion with this lower? Back of some inserts have a protruding screw at the top that could cause the marking.

2. Back of the BCG could have a burr, specifically around the groove for the buffer retaining pin. Deburr.

3. Buffer retention pin hole out of spec and too far rearward, preventing proper contact if BCG and buffer when closed. Check by removing receiver pins and sliding upper on to lower to see if BCG takes tension off buffer from pin. Answer: Special offset buffer retaining pins.

Primarily a cosmetic issue, but worse case is battering of buffer retention pin and hole.

That's what I've found so far.
 
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georgel said:
1. Do you use a .22 conversion with this lower? Back of some inserts have a protruding screw at the top that could cause the marking.
Click to expand...
I have, but it's probably not seen more than a few hundred rounds in this lower. I know the conversion has 1205 rounds through it but I don't track which lower that's in and I suspect much of that was berm blasting with the binary I had back in the day.

georgel said:
2. Back of the BCG could have a burr, specifically around the groove for the buffer retaining pin. Deburr.
Click to expand...

I went to look, and realized that the BCG that was in use is gone. 5421 rounds were fired out of the old upper with the out of spec BCG that kept blowing gas rings (in another thread somewhere). PSA replaced the entire carrier assembly and I never fired it again; retired the upper and replaced it with a much lighter weight unit. So perhaps that out of spec BCG was out of spec in more ways that one? There's nothing special about that buffer, I should have another one laying around or can get one and replace this one but keep the spring and everything else. if the problem clears up it was that old BCG, or old upper but either way those parts out of play.
 
I bet its the retaining pin hole out of spec. Have heard of it on too many Andersons. Get one of those offset buffer retaining pins.

You can always paint or sharpie the edge of that buffer and check after a couple of mags to see if the issue is still there with the new upper. Keeps you from chewing up another.
 
chrishf12 said:
You can always paint or sharpie the edge of that buffer and check after a couple of mags to see if the issue is still there with the new upper. Keeps you from chewing up another.
Click to expand...

That was my plan, see if the issue is actually occurring with the new setup and if not, get a new pin just preventatively as that one has been beat up and call it a day.
 
When you put the upper onto the lower put in just the front pin and slowly tilt the upper onto the lower. You should see the bcg push the buffer back slightly as you are lining the hole up with the takedown pin. That is the first obvious sign that a lower could be out of spec.

Normally those pins break way before 7k rounds. It's possible your pin is made of beskar or the bcg had/has a rough spot on it causing the finish to wear off. Normally when you see issues with retaining pins impacting buffers there are deep gouges in the buffer and it fails within 100 rounds.

All that being said, 7k rounds and if it is your primary ar I would swap lowers until I figured out what is causing the issues. I hate to be a brand snob but Andersons, BCA, and 80% builds seem to be the most common for out of spec lowers. Aero lowers are too cheap to gamble with breaking a buffer retainer pin when the crack head is trying to break into your house.
 
Could be an out of spec bcg, or lower. The buffer when installed should protude from the lower slightly.
 
Squanchy said:
When you put the upper onto the lower put in just the front pin and slowly tilt the upper onto the lower. You should see the bcg push the buffer back slightly as you are lining the hole up with the takedown pin. That is the first obvious sign that a lower could be out of spec.
Click to expand...
The recommendation to remove the take down pins and slide the upper into position was to make the contact more obvious. There should be a little spring action going on.

I'm starting to wonder if the BCG is making some contact with the buffer retaining pin during cycling and "driving" the pin into the buffer. But, I guess that would also show up on the bottom of the buffer tube.
 
Jayne said:
All the way around it's marked up from hitting the retaining pin. This lower has ~7k rounds through it.
Click to expand...
I'd be more concerned with the marks in the center of the buffer.

To me it looks like the buffers edge contacted the BCG when putting the upper on the lower. This would scrape the coating off resulting in the OP picture.
 
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buffer.jpg
I pulled out my highest mileage buffer. Probably a similar round count to yours if not more. No chatter around the edge, just finish wear on the face.
 
had an example many years ago with similar problem, i machined the outer perimeter of the buffer so it would clear the pin in operation, but the
pin would retain the buffer on takedown. it still functioned ok. the hole for the retention pin was out of location. the relief's diameter
still allowed contact with the carrier surface.

it was a really cheep full AR and is long gone now.
 
Jayne said:
All the way around it's marked up from hitting the retaining pin.
Click to expand...

With AR-15 ~ 10, using a Conventional Buffer System , the purpose of the Buffer Detent Pin is to keep the buffer install with the receivers are opened ~ split.

With the receivers Pinned together the Buffer should not contact the detent.
This means the BCG is / will be in contact with the buffer and it is not much of a , pre-load, if you will.

Any AR, big or small, that has the buffer in contact with the Detent, while closed, means something is out of spec and it does not matter how much or how little was spent purchasing the receiver~s and related parts. Concerning cost, I mean this literally whether $90 or $300 plus was spent on upper and lower receiver~s.


C-doodle said:
From what I have read the only real failure point is if the little nub breaks off and falls into your fcg.

If your worried about it just remove the retaining pin.
Click to expand...

So True, run without the detent.

What's the fix?
Determine what is out of spec, the carrier, upper, lower?

Besides removing the Detent Pin, another walk around is to fashion a piece of material that inserts into the rear of the BCG to take up the clearance, and typically will not be much.

Somewhat related to this, not directly related for the clearance issue, is to use a Long Tail Buffer Tube or AKA an Enhanced Buffer Tube for the longer tail. This tail will help guide the BCG better than the Flush Cut Tubes will.


Enhanced Buffer Tube.png


Safe Shooting

​

 
I’m no expert, but it looks like your rifle might be a bit over gassed based on the “impact” witness marks, you might be able to clean up the gas impingement ports & tube.
 
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It looks like there are several solutions that can work, offset retention pin, milling the buffer, adding something to the rear of the bolt.
Personally, the special retention pin seems easiest.
It would be nice to determine the actual "problem".
 
I have a BCG & Buffer that is not preloaded properly.

It has been right on the edge just enough and there are marks in the area of the detent pin.

For now my fix is to install a rubber stopper in the carrier and run a wood screw through the middle.

There's enough arch in the screw to crown the stopper out over the carrier.

After 8 ~ 10 rounds this temp(?) fix is holding.
Prior to this I used a half inch long 10/32 set screw and after one round the stopper was pushed flush with the carrier.

buffer 3.jpg
 
Y’all are killing me. What the fook is this hillbilly nonsense.
 
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