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Posted: 6/1/2006 1:18:55 AM EDT
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The marks on the buffer occurred after using the following bolt carrier for the first time. I have never seen this happen before. I am certain it will not affect functionality, but I would like to know how it happened. The following pictures might describe it better. They're a bit blurry, sorry.     
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OK, you guys kill me when you post photo's during the day. Lets just say that dail up sucks big time, and how I log onto the site in the morning (have cable at night). Problem is that the back of the carrier has a bur(s) at the slot for the buffer retainer (U channel), and the milling bur(s) needs to be filed down/ sanded flush so the back edge of the carrier is smooth. |
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It shouldn't be the buffer retainer. When assembled, the carrier should be pressing directly against the buffer and forcing it back slightly. The only purpose of the retainer is to hold the buffer assy. and action spring in place during assembly. My guess is the burr. It isn't normal or else EVERY AR variant would have it, yes? In fact, I contacted BM about this very same issue a couple'a years ago with said burr being the culprit. Suggestion from them was to try pulling tissue paper around the back of the carrier to find the burr. Absent that, I'd use some liquid blue and see where it's worn on the next range day. |
Just between you me and the fence post, I'm for giving abnk some credit here, thinking that a "burr" on the rear of the carrier would be something easily detected by simply rubbing one's thumb over the rear of the carrier. I'm of the opinion he'd have noticed something so easily located. One thing missing from this post however is background on the lower. There is no brand name, no information on whether we are talking about a factory produced lower or a self-built, (the fact is abnk may not even know as this could have purchased off the EE here or anywhere). The "point" being we know nothing about the background of this particular lower. That said, not all lowers are equal and like it or not mistakes in manufacturing are made. Shit happens, buffer retaining pin holes get drill outta place minutely, or drilled at an imprecise angle on occasion, either of which can cause these marks. Heck even the buffer retaining pin "part" itself may be outta spec as not all parts are equal. IMO for whatever reason (and mostly because of the marks themselves, in their appearance) it appears to me through contact between the carrier and the buffer retaining pin itself or contact between the buffer and it's retaining pin, I'm gonna stick w/ Dragonfly's opinion. I think he's right. Note: proper examination of ALL the parts here will best lead to the determined reason for these marks and pictures of ALL the parts are not available, hence we cannot see exactly what the "tit" on the BRP looks like or even how the lower set-up appears when all parts are installed. YMMV, but speaking plainly "sometime the advice and information ya get, is in direct proportion to the amount of data and information provided", in other words we're all just guessing here based on very limited input......  Mike |
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The small "chipmunk bite" marks that run around the circumference of the buffer would be from the buffer hitting the buffer retainer. The retainer is the little detent that prevents the buffer from flying out when you shotgun the receivers. It is NOT normal. It occurs with out-of-spec lower receivers that have drilled the retainer hole too close to the rear edge of the receiver, preventing the buffer from protruding enough. On a properly made lower receiver, the buffer will protrude enough that when you close the upper receiver, the bolt carrier will actually PUSH BACK the buffer as it closes. That prevents the buffer from hitting the retainer each time the carrier slams home. Any other marks on the inside part of the buffer face is "normal" (circular marks). It's from carbon/powder buildup and wear against the bolt carrier. |
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See shinny spots at the 7:00 and 1:00 of the U channel? These are the areas that are sitting high/bur'd; the wild chipmunks that are chewing away at the buffer face. Buffer retaining pin damage is a straight line that goes from the very edge of the buffer (read deep and a straight line, and the groove/marring gets less deeper towards the middle of the buffer (the pin being bent). |
if you're really that worried about it, there's a plastic disc that you can buy that sticks to the front of the buffer and will take all of the punishment. i forgot what it is called but if you search for it on the internet, you're bound to find it. hope this helps.
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OK, mr_wilson gave me too much credit. The shiny spot that Dano mentioned is, in fact, a burr. It is so small that I cannot even feel it with my fingertip--except for maybe a feminine pinky. When scratching it with a fingernail though, I can feel it and I can hear a little flicking sound. I would never think that a burr so small can leave such ugly marks, especially in one shooting session. Thanks for the help, gentlemen. 
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Agree. The burr can be so slight that it can only be felt when you rub your lips across it. But, do not under estimate the damage that this slight burr can cause. The burr can be anyplace indicate by the arrows. Take a small file (jewel file) to round-off the edges. 
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