Hey guys,

Just took my new Armalite M15A4 (14.5" barrel) out for an initial breakin period.  It is  brand spanking new and came from the factory as a complete carbine.  After I got home and started cleaning it, I noticed that the buffer face (the area that contacts the back end of the bolt carrier) appears to have some scratches on it (the scratches are definately from the carrier as they are in the shape of a ring - approx. as big as the rear face of the carrier).  I've owned and fired several AR's in the past and never noticed such wear on the face of the buffer (on a new rifle or carbine).  I can see this possibly happening over time (with the buffer continually contacting the end of the carrier during the cycling process), but I didn't expect it to happen after only firing 50 rounds through the new carbine.  Anyone have any insight into this?  Did I just get a soft buffer?  Is this common with Armilite carbine buffers?  Thanks in advance.

hsld.

BTW.  I've been thinking about getting a Colt H buffer to replace the one in my carbine.  The one in my LE6920 appears to have a better finish (anodizing?) than the buffer in my Armalite...  

Yeah, a lot here will tell you that it's normal, there was a similar thread over at Tactical Forums one day.
[url=http://64.177.53.248/ubb/Forum56/HTML/000497.html]AR15 deficiencies[/url]
That said, my Colt GM has A LOT of rounds through it and there is no wear on the buffer, none.

Some wear (not damage) can be considered normal since there may be a rough spot on the rear of the carrier. If it's not a rough, or high, spot on the carrier then often it's a mismatch (angular) between the upper and lower. In effect, the carrier is not coming directly to the rear compared to the bore line. When that happens one edge of the carrier contacts the buffer face first.

If you see dents arranged radially about the circumference of the buffer's face then you have trouble.

The wear/damage will always be radial bc the buffer spring rotates slightly with each compression.

[ed for speeling]

I've found that a lot of carriers need to be slightly deburred around the inner and outer circumference of the rear face. Just a touch with a Dremel or a fine file. Just enough to break the sharp edge.

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My Bushmaster M-4 type does this also.

It doesn't seem to effect the operation in the least. The buffer appears to be made of a lighter material than the steel carrier.

[url]http://www.m16clinic.com/buffpad.htm[/url]

Thanks for the input guys.  No, there aren't any "dents" in the outside circumference of the buffer face (possibly caused by the retaining pin abnormally contacting the edges of the buffer ?).  The scratches (in a circular pattern) start a few millimeters in from the outside circumference and appear to be consistent with the end of the bolt carrier coming into contact with the flat surface of the buffer.  I did have a look at the end of the carrier - it does appear to be somewhat "rough", but I didn't think it would be enough to cause such wear (at least not so quickly)...

hsld.

hsld,

Yes, if the bolt carrier ass'y sits too far forward in the upper the buffer is allowed to stop on the buffer retaining pin when the bolt is in battery. On a properly set up piece the rear of the bolt carrier will push the buffer off of the buffer retaining pin when you pivot the upper closed onto the lower. You should be able to feel this added bit of tension if you close the parts slowly. Sometimes you can hear the buffer spring compress. The buffer should rest against the rear of the bolt carrier at all times.

If this setback does not happen the buffer will slam into the buffer retaining pin with each shot. This leads to many different problems.

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My feeling is that this is normal wear and part of the design, hsld.

In my view, one wants the wear of shooting such high power cartridges limited to such easily replacable parts such as the buffer etc.....

However, I am not aware of hearing that buffers fail, irrespective of how much cosmetic scratching occurs to the face of the buffer.

Just consider that cherry busted.

My .02 cents.

Thanks again guys!  Figured it was nothing to worry about.  Just needed to hear it from someone else I guess...

hsld.

This is the face of my buffer.It's obviously got some problems.This is after firing about 90-100rds today while sighting in a 14.5" DPMS M4 upper I bought used.How can I narrow down the problem(s)?

Redbone,

Are those dents in the face of your buffer? Ones you can feel with a fingernail? About an eighth of an inch long aligned radially with the center of the buffer?

When your bolt carrier ass'y is fully inserted into the upper is the rear of the bolt carrier flush with or slightly above the rear of the upper? When you close the upper onto the lower can your feel, or hear, the buffer being slightly compressed into the buffer tube?

If it's just finish wear, look to the rear of your bolt carrier for a high spot or a burr. As gus posted the notch in the bottom of the carrier is often the culprit.

Yes.



Yes, it's flush.



Yes, but ever so slightly.



It's definetly caused by the buffer retainer spring.

The rear of the bolt carrier should be flush with, at a minimum, or slightly above the rear of the upper receiver for proper function.

If the carrier is corrrectly set then there is a chance the pin hole for the buffer retaining pin is mislocated. The buffer should extend from the front of the buffer tube ~.062". If you need a tighter number I can dig out the prints.

These two causes are the biggest reasons for that damage. A combination of several other factors can also be to blame.

[s]Send it back to Armalite.[/s]


[that was hsld's rifle]

The upper is a DPMS as well as the bolt/carrier.The lower is a PWA but the buffer that came with it was not marked up until i attached this upper.In a post on Tactical Forums you mentioned that the barrel threads may be too long and could possibly cause this problem? I'm also wondering if cheap lower receiver parts could have anything to do with it?The parts in this PWA lower are not the best(quality wise).

If the threads on the upper are too long then the barrel sits too far forward and the bolt carrier sits too far forward and the rear of the carrier is not flush, or above, the rear of the upper.

The entire upper may sit too far foward due to mislocated takedown and pivot pin holes. Or it could be a combination of tolerances.

Had the PWA lower been fired before?

Redbone - If it was OK in that lower with another upper, are you using the same bolt/carrier as you were when it was OK or are you using a different one for the new upper? If you're using the same bolt/carrier, then the upper or the barrel extension is out of spec. If you are using a different bolt/carrier, then it could be either the upper, the bolt/carrier, or the barrel extension. Clearly, the rear surface of the carrier is not located far enough rearward when in battery and is allowing the buffer to make contact with the retainer pin.

If it was doing that with the old upper as well as the new one, the buffer retainer pin hole is mislocated.

The PWA lower is new to me and this was the first time I fired it.I'm sure it's been fired before.The DPMS upper and DPMS bolt/carrier are also new to me.The upper is used but the bolt/carrier is brand new.I don't think the buffer retainer hole is out of spec because the buffer that came with it had no marks like it has now.I know it's possible that the person that sold it to me could have changed out buffers but I don't think so.

Ok, I replaced the original buffer with a Colt H buffer and it's still marking upp the buffer.I'd like to fix this problem asap.I don't have another bolt carrier to try out but I'm wondering if it's possible that the DPMS bolt carrier is too short?It barely sits flush with the upper receiver but it does seem to push back the buffer when i close them together.If the lower receiver is out of spec, how can I go about fixing it? It's a preban PWA.

I gaurantee that you will fix this problem by filing the edges of the carrier as shown above with red arrows. Be sure to round the corners as shown with green arrows.  Do not under-estimate the harmful effects of a very small burr.  Use your lips to feel this area.  For me, I have had burrs so small that I could not feel it with my finger, but I could feel the burr against my lip (then , it felt slight).  This very small burr "went to town" on my carrier.  I now deburr all of my new AR's before I ever shoot it for the first time.

I think you're right.I can actually see the burrs sticking out on the carrier.I'll file them down in the morning and see what happens.It makes sense since the buffer marks are exactly where the burrs are.Thanks!

The pin hole for the buffer retaining pin must be mislocated on my second lower.  This is the lower that has the 3-4 "dents" on the edges buffer face, which pefectly match the width and height of the freaking pin!

So from where to where do I measure so I can tell if it's out of spec?  

From looking at both lowers, it seems that the buffer tube on the one that DOESN'T exhibit the dents is closer to the post of the pin.  On the lower that does have the dings the buffer tube seems a BIT further from the pin...I can see the fourth thread on this sucker more clearly than I can on the lower that DOES NOT have the dings...DOES THAT MAKE SENSE? It's hard to describe...this sure is aggravating...

Even buying a COLT upper will not solve problem as it's related to the damn lower...

From the back of the lower to the [b]center[/b] of the buffer detent hole should be 0.565" +/- 0.002". Hole diameter should be 0.255" + 0.006". Mic the diameter of yours first then use half D. The hole is tilted 6 degrees so there is a little slop when measuring to the edge of the hole, if you've got plug gages you can use those to make up the slop.

Can you see/feel/hear the buffer move back off the detent when you close the upper onto the lower?

If the pin location was causing the dents then the pin hole would be further away from the rear of the carrier aka closer to the face of the buffer.

Thanks for that pic G35!  I went out and bought myself a set of hobby files and did the same thing to my carrier...

hsld.