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Posted: 7/30/2017 7:48:18 PM EDT
This is a pic of my nephew's AR. He just noticed it and sent me this pic. I haven't seen it in person yet. What could cause this wear around the edge of the buffer? Thanks.
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| Happened to me before. Most likely a burr on the back of the bolt carrier. That's what it was for me. Easy way to tell it's not the buffer retainer pin is to watch the upper and lower close. You can see the bcg push back on the buffer right before it shuts all the way. Then you know it's not even hitting the pin. |
| I've had this problem before and I'd be willing to bet it's due to the buffer retainer, but in reality the lower is out of spec for that hole. You can tell him to either chuck the buffer in a lathe and knock down the edge or purchase an offset buffer retainer pin. I wouldn't run that rifle until he does one or the other. Commonbullets.com offers the offset retainer. Other than that, a different lower. |
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Check the buffer retainer first, sometimes they sit too far back in the lower as mentioned and the buffer hits it with every return stroke.
However, in my experience, this is more often caused by a burr on the rear of the carrier. It usually at the hard, straight edges of the buffer retainer pin channel as shown here. The reason the marks traverse the circumference of the buffer face is because it will rotate a bit with each cycle, so the marks eventually cover the whole way around. 
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Quoted:
Buffer retainer hole drilled to far back? Are there noticeable wear marks on the buffer retainer pin, like the buffer is hitting it? The best solution short of band-aiding, is to sent the lower receiver back for a replacement (one which the buffer retainer channel is correctly located instead). 
1. is the buffer tagging the buffer retaining pin since it channel was drilled too far back in the lower receiver. 2. is burs on the back of carrier edges. 3. is a Bur on the back bottom of the U channel of the carrier |
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