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Posted: 5/27/2007 3:54:19 PM EDT
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I went shooting today with my 3 newly built lowers and ONE upper. After I got home I looked at each of my lowers, and they all had this problem in the pictures. It looks like it is chipped by the buffer retainer pin. There is also a crescent shaped line chipped out like something is digging in. When I put the upper/lower together, the bcg pushes back on the buffer just a little bit (maybe 1-2mm), is that normal? The pictures of are 2 different lowers, the other one is the same. The marks look like they are in the same spot. This is happening on all 3 lowers with a CAA 6 position collapsible stock. Any ideas? Thanks Eric  
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Eric, check for a burr on the back of your bolt carrier. Yes, it is normal for the BCG to push the buffer back a bit, that is why it is probably not the retainer causing the marks. The buffer does not actually make contact with the retainer with the rifle assembled. I think you will find a rough spot on the carrier, or something stuck to it. 
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Where you policing your spent brass, and how many of them where missing primers? As stated, the impact marks for the most part are coming from the inside edge of the back of the carrier, and if no high edges/burs are to be found (normally at the bottom U channel cut for the pin), then suspect loose debris (like primer parts) in the action (between the back of the carrier and the buffer) doing the damage. If you suspect blow primers from a bad lot of ammo, pull the FCG's to check for pieces hiding under the triggers (they can cause all kinds of havoc, including locking up the trigger). |
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I checked the back of the carrier before I did anything, and didn't see/feel any burr or anything. After you guys kept pointing this out, I did a closer inspection and realized that there was a small shiny point where the carrier is cut for the retainer pin. I took some sandpaper and smoothed out the edges then dremeled it with a polishing tip. Then I pulled the charge handle back, held the bolt catch back, then let her slam home about 10 times. I saw no marks. Is this a case closed? Did this solve the problem, because the marks usually happen when the bolt slams home after catching a round right? thanks |
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Well, when the bolt "slams" home there is a lot of force applied to the back of the carrier by the momentum of the buffer. My guess is the marks are left more by the repeated travel and pressures of the functioning rifle, because the carrier "rides" the buffer back and forth. I bet it solved your problem though.
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