i have about 200 rounds in this build, and when I took it apart to clean it today I noticed some marks on the buffer. Can anyone tell me if this is normal or what I need to do to fix it?

Buffer:
http://i1228.photobucket.com/albums/ee451/wildcatdd/IMAG0249.jpg


Back of bolt:
http://i1228.photobucket.com/albums/ee451/wildcatdd/IMAG0253.jpg

Normal wear

Normal....nothing to worry about



 

It's pretty typical. There might be a small burr on the BCG that you could lap off to reduce the wear to the buffer face. It's not a big deal though.

No worries

Just shoot it

Shows you have been shooting it.

Damn, 32+ years of experience and the FNG gives the correct answer.

Go figure

Remove the buffer detent....

Take a flat stone and polish the rear of the carrier.

The marks on the buffer will soften or disappear.

The carrier doesn't come in contact with the detent.

The buffer only contacts the detent when the BCG is removed, or the upper is shotguned

That doesn't look like damage from a "burr" on the rear of the carrier. It looks to me as if the buffer is coming into contact with the buffer retainer.

no but the buffer does

It Shouldnt when the upper is attached. When you attach the upper, the BC should push back the buffer slightly and relieve tension from the detent pin.

Yes, it shouldn't, but some rifles do, and it looks as if the OP's is one of them.

Similar thread...link below.

looks like contact with buffer retainer to me also... not carrier

http://www.ar15.com/forums/t_3_66/524295_.html

And it definitely isn't "normal" as suggested by many posters above.

That thread is very similar to my situation, and from what I can tell in the thread the fix is to replace the lower. The lower I'm using is a Surplus Ammo Arms lower, I thought they were pretty good - Is there anything else I can do to fix this short of getting a new lower?

I'm impressed with these new guys
http://www.ar15.com/forums/t_3_66/470291_Help_me_diagnose_my_buffer_damage.html

While some wear on the buffer face is normal, 86HMMWV is absolutely correct in his diagnosis. That wear is the result of an improperly drilled buffer retainer hole. It's a pretty common issue.

The buffer retainer is nothing more than a convenience item, to prevent the buffer and action spring from departing the receiver extension tube when the rifle is opened. When drilled properly, the buffer should back off of the retainer when the rifle is closed. The OP's buffer wear isn't the result of a burr, the pattern and appearance of the wear after only 200 rounds is the tell.



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Well crap...
As my first build I'm disappointed that I've encountered such a problem with my lower...I wonder if I can contact Surplus Ammo Arms for a replacement. For the time being I guess I'll take out the retainer all together since I don't want to chance having the retainer break off and bounce into the upper.

HERE

HERE

Upon further inspection, I can definitely see the carrier push the buffer back into the tube when assembling the upper to the lower, so I will try this despite not seeing any marks on my carrier. I should also note that I have no looseness or gaps of any kind between my upper to lower.

If your lower is out of spec, the detent will get abused and it may snap off in time. The BCG should lean on the buffer when the receivers are closed, so there is no tension on the detent. The detents only job is to hold the buffer inside the buffer tube when the receiver is open.

VERY normal, if you don't have those marks, you're not loving (shooting) your rifle.

Uhhhh, NO. Leave it the fuck alone.

I can definitely see the BCG lean on the buffer and a gap between the buffer and the detent when I close the receivers. Maybe it's a burr on the BCG???

Yes, I think so. Clean it up with a stone like the link shows.

ETA2:.....see follow up post below to this one

ok, I'm probably going to get crapped on for this reply.

I have the same issue as you on one of my AR's.  Spikes upper and BCG on a DS Arms lower.  After looking at the replies here it go me thinking.

When I was assembling my lower, the extension tube has a lip (non-threaded area) to start and then normal threading.  I threaded it in until it held down the retaining pin.  I could not make a further turn without it starting to bind on the pin itself.  I was ~1/4 turn short of the next full turn.  This caught the pin fully on the flat right before it started to round up to the smaller part of the pin.

My impacts look very similar to yours.  Right at the outer edge of the buffer all the way around.  Seems to be just enough to take off the paint (anodize) and a very small bit of metal.  

Before you junk everything and start over.  Try this.

Remove the lower and buffer.  Break open the nut on your extension and see how close you are to being able to go another full turn into the lower.  If you are close, remove your extension tube and file it down a bit on the lip.  I'm only talking a thousand's of an inch.  Use a FLAT FILE and leave the dremel in the case.  Keep filing and testing till you can make that next turn and lock it down.  The point here is to bring the extension a bit further into the lower and get it to ride directly on the PIN of the retaining pin itself and not the flat or lower part of the shoulder.  Two things I think are being accomplished here.  #1 The pin is going to ride a very little bit lower, but not enough to matter.  #2 is that you are going to force it - without it being in a bind - fully to the forward side of the hole.  I think this is the more important objective so only remove enough material from the extension to get that next turn, but don't leave so much that the pin is in a bind either.

Take a Sharpe marker and fill in all the marks on your buffer.  Shoot it and/or cycle it by hand.  If its still hitting, it should nick up the buffer again, but I don't think it will.  (If it does still hit, you are at least stuck at the same place you were and it only cost some time and a bit of aluminum from your extension that doesn't matter. )

This is probably an issue of tolerances in the pin, extension or lower.  Just getting that pin moved just a bit forward may be all it takes.

ETA:  I did this to mine and its not leaving any marks now by manually cycling it.  I'll try to shoot it tomorrow to be sure.

As it sits right now I can see a gap between the detent and the buffer, so if my problem has to do with a burr on the BCG, won't this make the problem worse? Although, as I think about my build, I believe I do remember that I could almost turn the tube a bit more if I filed the tube a bit. Let me know how yours shoots tomorrow!

Oh yeah! THere's one way to correct that...

SHOOT IT MORE.

That's good if you can see a gap, but do this to make sure: pull the charging handle back and let it fly, just like you would when charging the rifle. Can you still see a gap then?

Please do this and report back. For your sake, I would like nothing more than to be wrong

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I cycled it a few times and I can still see a gap. It's a really small gap, I'm not sure how big it should be, but there is definitely a gap.

Fair enough, and that's good news

Ignore what I said earlier.

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I agree with the guys that told you that it was NOT normal.  I don't want to try and scare you into believing it's something serious because I truly don't know.  What I do know is that I have over 1500 rds on my complete rifle and my buffer shows almost no wear.  Definitely doesn't look like your pics.  Take what I say with a grain of salt.  YMMV.

Why does everyone automatically say it's the lowers fault for having the detent pin slightly off.......there are two areas on the upper that can affect hitting the detent pin.  First are the upper retainer pins and second is the torque shoulder for the barrel nut.  Both if out of tolerance can cause the buffer to hit the pin.

Advntrjnky

Here's a pic of a buffer that has seen a number of new uppers and BCG pass in front of it.  To see some wear on the face of the buffer is normal unless you want to polish the back face of ALL your carriers.  If however your buffer is hitting the buffer detent that is NOT a good thing.  The OP buffer is NOT hitting his detent though.  About the time he has made note of the  marks on the buffer.  The burr has peened it self out for the most part.  OP what your seeing will not affect the function of your rifle one bit

A well used buffer

Here's a pic of my Colt 6920 buffer after only about 50 rounds:




This was the result of a tiny burr on the end of the carrier, at the U. The chatter marks around the circumference were made as the rifle was fired, and the radial scratches happened when I opened or closed the lower and the burr dragged across the face of the buffer.

Took only a few gentle laps of the file to clean it up and the marking stopped.

.
.

I had a similar problem where a bcg was eating up my buffer, didn't effect performance, but I did get one of these pads to prevent further damage: http://www.brownells.com/.aspx/pid=19699/psize=48/Product/AR-15-M16-AR-10-AR-BUFFER-PAD

Has worked well so far.

He may be new here but that does not mean he has to be new to AR15s

OK a burr like that I can see doing something about

Thanks for all the info and pics everyone!

Reef - are you sure there's no way it could be hitting my detent? After looking at the detent a little closer I can see the tip of it does seem to have some wear on it. Is there anyway I can test if the detent is making contact with the buffer other than visually inspecting it? Is it normal for the detent to have some wear to it? (when I say wear, I mean the tip has some of the bluing worn off and it is very slightly rounded a bit). The wear on the buffer seems to correspond to the placement of the detent.

Someone mentioned earlier that the upper may be a culprit as well - can someone tell me how I can check if the upper is causing this?

OP  

in your photos I can see a small burr on the rear of your bolt carrier.  At the flat at the bottom of the detent clearance notch.  This burr is banging small dents into the buffer face, it makes a circle as the buffer clocks during firing.  This damage is not normal, but will not ruin the buffer.  After time it will pretty much self limit as the burr is only so big, and the flat of the carrier limits the depth of the denting.

BEFORE you replace anything else.  Feel the back of the carrier, if the burr can be felt, clean it off with a stone or fine file.  Just enough to remove this burr, no more.

I believe that will solve your buffer damage problem.

Don't get all rushed into a new lower or something.

I'm not completely convinced that the carrier is causing the problem. If there were a burr causing this, it seems like the damage wouldn't be so far on the edge of the buffer. It seems to me the 'circle of damage' on the buffer would be a tighter circle and more towards the middle of the buffer rather than the outside edge.

This pic looks like carrier damage - it's a tighter circle and you can visually see the damage clears the detent and looks more like the size of the carrier. I don't think my damage is similar - my damage looks like it lines up with the detent and it is occurring on the outside edge where the carrier wouldn't be able to hit the buffer.  

Here's a better pic. To me, you can see where the damage lines up almost perfectly to the detent.

http://i1228.photobucket.com/albums/ee451/wildcatdd/IMAG02591.jpg

You are correct.  Your detent is definitely making contact and I don't care what anyone else says.  I think you know that too.  Of course, you're looking at it first hand, so you have a better handle on it than any of us.  I think you are on the right track to admitting where the problem is.  Now you can take the steps to fix it.

This is a follow up to a prior post.  I'm having the same issue as OP.  It does seem to be strikes of the buffer on the retaining pin.

Spikes upper, BCG and H2 buffer.  DS Arms lower with a PSA parts kit.  I think the extension is a DD.

First pic you can clearly see where the dings are lining up with the post.  The second pic is where I have filed down the extension to get an extra turn out of it which I had hoped would make the pin ride forward a bit more.  Doesn't seem to have worked as you can see where the marker cover up I used has been rubbed away after firing another 60 rds.  Wear in the last pic is at the 6pm position and ~11pm and I had filled in all the markings prior to use.   Sorry for the cell pic's.  Best I could do up close.





Right now my plan is to just monitor it and keep using as is.  The dings are not that deep and don't seem to be getting much deeper.  I can see where the BCG is making contact with the buffer, but obviously not pushing it back enough. Doesn't seem to be striking the pin that hard as there isn't significant impact damage to the buffer or pin.  That makes me think this will self limit as some point (before the pin breaks!).

Take another look at the pic of the buffer I posted.  The WEAR is right to the edge.  I would have to say its NOT your detent that's making the marks.  I have seen buffer that were hitting the detent before.  They left lines that pointed to the center of the buffer.  The detent gets wear at the tip from the action spring passing over it when it was installed.  If this troubles you that much wait till you see the bolt cam pin after about 1000 rnds
Oh and the carrier rides all the way to the edge.

ETA some of those dings seem to go above the detent. Closer to the center of the buffer.