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Posted: 5/15/2012 3:29:57 PM EDT
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A little over a week ago, I went out and shot my 10.5" SBR. I shot 60 rounds of Lake City M855 and 30 rounds of Privi 55gr FMJ. I didn't have an issue while shooting, nor have I ever. I've shot about 600 rounds through this gun so far.
Well today I took the upper off the lower and my buffer and spring shot out. I noticed the buffer retaining pin rolling on the floor and the retaining pin spring was in the fire control pocket and was mangled up. I picked up the retaining pin and noticied the tip of it was bent. I check out my receiver extension and noticed the lip that holds the pin down has a dent from part of the pin. I currently have an H buffer. I probably should go heavier, but I didn't have issues previously. Any ideas as to what the cause is? Sorry, I didn't take pics It's an easy fix...it may cost me $5 is small parts or $60 to just replace parts thet may fail or cause failure in the future/ Receiver extension is a BCM LPK is CMT |
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Quoted:
But the bent tip on the pin? Seems like the carrier is supposed to hold the buffer back a bit so the buffer doesn't slam the buffer retainer pin on each cycle. The retainer bore may not be in the correct location or the carrier may be out of spec in regards to length. When you put it back together make sure that the buffer tube is screwed in as far as possble with binding on the retainer pin. When you close the upper you should notice a little "push back" on the buffer as you close. |
| ...or the receiver extension was not holding the retaining pin down far enough, and the carrier bent the top of the pin. Either way, that receiver extension tube needs to be in far enough for the cut out in it to retain the buffer pin. This should be extra easy, because if the tube isn't in far enough, it's almost certain that the castle nut isn't so snug that it'll be difficult to turn the tube in a turn or so. Once it is in far enough, tighten the castle nut and either LocTite it or stake it so it keeps the tube in place. |
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Quoted:
When you close the upper the back of the bolt carrier must push the buffer back a fraction of an inch so it does not rest against the retaining pin. The buffer only touches the retaining pin when you open the upper. This. I mentioned this a few posts back. Almost seems like something is out of spec to have bent the pin on the retainer. |
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