View Full Version : Broken Buffer Detent- Retainer.
While taking the upper off I noticed that the buffer detent was sheared right off. The lower only has around 3k through it, but the detent is a stock CMMG. The buffer tube is the A5.
The buffer has this knick on it:
Is that normal wear?
I am not sure if something is going wrong when the gun is cycling, or it is just a random break.
Does your brass look okay? Any other functional problems? If not I'd just say one of those things. Is it possible you may have scratched/scored the detent pin when you installed the A5 tube? That might have created a place for it to break. Also check the milled groove on the bottom of your bolt carrier to make sure it isn't gnarled up. Regardless of what went on prior to the spring pushing the buffer forward, the spring only exerts so much pressure - that is why my money is on just a thing.
Brass looked fine, the BCG is good, and the gun functions fine.
I just ordered a Colt detent from Brownells. Though I paid a lot more than I wanted to.
mebiuspower
10-12-14, 21:05
Could have bought a heavy duty one like the one below?
http://www.leitner-wise.com/collections/parts/products/heavy-duty-buffer-retainer
29003
The buffer should never touch the detent unless you are removing the upper receiver. I hadn't ever seen a broken one, but I knew a Team Sergeant that wouldn't run the retainer at all because of the possibility of its breakage jamming up the gun. His theory was why have a superfluous part that does nothing to make the weapon more lethal, that can break and deadline it.
I put this out of my mind until shooting last month when a friends had this exact issue occur, and the tip of the retainer ended in the lower and prevented the weapon from being put on safe.
Rick
The buffer should never touch the detent unless you are removing the upper receiver. I hadn't ever seen a broken one, but I knew a Team Sergeant that wouldn't run the retainer at all because of the possibility of its breakage jamming up the gun. His theory was why have a superfluous part that does nothing to make the weapon more lethal, that can break and deadline it.
I put this out of my mind until shooting last month when a friends had this exact issue occur, and the tip of the retainer ended in the lower and prevented the weapon from being put on safe.
Rick
I have no idea if the buffer is touching when assembled. I just happened to see it broken today, no other signs of something going wrong. Just that knick in the buffer.
I was always told to stay away from DPMS/CMMG LPK because they weaker steel in kits.
When you install a new buffer detent pin check to see if the buffer is protruding from the lower like my image below. If it isn't, that means that your buffer detent hole is drilled too far towards the rear of the receiver and the lower is out of spec.
http://i24.photobucket.com/albums/c19/FaRKle0079/guns/BCM_Lower_zpsf9a8df42.jpg
Here's a pic of an out of spec lower, the buffer is not visible:
http://i24.photobucket.com/albums/c19/FaRKle0079/guns/TNArms_Lower_zpsfeebaf89.jpg
When the upper is closed on the lower the rear of the BCG should push the buffer off of the detent (you can see this if you look into the gap between the receivers while closing the upper on lower). Thus, the buffer should never touch the detent while the receivers are closed together.
You'll also notice your buffer edge starting to get chewed up if this issue occurs. Here's a pic of my buffer that was in an out of spec lower:
http://i24.photobucket.com/albums/c19/FaRKle0079/guns/Buffer_Marks_zps87f30fb7.jpg
The mitigations for this are to get a Tubbs carrier weight system which effectively extends the rear of the BCG, or to take a 1/4" drill and extend the detent hole forward towards the fire control pocket till the buffer comes far enough forward. I took the 2nd route with my lower and used a piece of blister packaging as a shim to keep the detent forward.
Robb Jensen mentioned running the gun without the detent as an option. Kind of a pain to open/close the receivers, but it's an option.
I would NOT keep a lower like this however.
sinlessorrow
10-13-14, 09:50
The buffer should never touch the detent.
If it is an in spec lower the bolt carrier will push the buffer a little ways into the extension and keep it off the detent. Out of spec lowers allow the buffer to strike the detent.
Alright, I will update this thread once I install the new detent. Thanks everyone.
Okay, have the new detent:
The buffer does have some dents in though (the picture above in the OP shows it)
Comparison with a S&W lower with around 4k on it, also with an A5.
I also checked and the BCG does make contact with the buffer.
So it seems that this lower is in spec, to me. Is it safe to torque down the nut and stake it?
Robb Jensen
10-17-14, 16:49
Another option is to use the new JP captured buffer assy which doesn't require a buffer detent. Personally I'd get the lower replaced by the manufacturer.
Another option is to use the new JP captured buffer assy which doesn't require a buffer detent. Personally I'd get the lower replaced by the manufacturer.
Why? If it is in spec, which it seems to be, then it should be good to go right?
It could be that your carrier is short as well.
The lower looks OK. Can you see the carrier pushing the buffer off of the detent?
The lower looks OK. Can you see the carrier pushing the buffer off of the detent?
Yes. I can feel it as well.
Yes. I can feel it as well.
Hows the rear of the carrier look? Is it really rough? I've seen carriers scratch the buffer at the corner where the hollowed out portion is, but never the whole face of the rear of the carrier before.
Hows the rear of the carrier look? Is it really rough? I've seen carriers scratch the buffer at the corner where the hollowed out portion is, but never the whole face of the rear of the carrier before.
The rear of the carrier looks fine. It I am assuming when the detent broke it got between the carrier and buffer and caused that.
Robb Jensen
10-17-14, 22:23
Why? If it is in spec, which it seems to be, then it should be good to go right?
To clarify. Yes IF the lower is in spec then do nothing. IF IT'S NOT then have it replaced, OR run it without a buffer retainer OR use the JP captured buffer assembly.
BTW your buffer with the large worn ring around the outer edge is caused but a rough edge/burr or finish on the back of the carrier.
To clarify. Yes IF the lower is in spec then do nothing. IF IT'S NOT then have it replaced, OR run it without a buffer retainer OR use the JP captured buffer assembly.
BTW your buffer with the large worn ring around the outer edge is caused but a rough edge/burr or finish on the back of the carrier.
Thanks for clarifying.
I had a CMMG buffer retainer detent snap in half also. It happend like a month ago, I changed all lower parts for DD parts as the CMMG LPK was the only LPK I could find during the panic. Lesson learned, not that if could not happen on any LPK but I have not had all that many rounds through the build. Also my buffer looks to be in good shape. The detent snapped upon disassembly of lower / upper to put into my range bag, so I am assuming the pin only got pressure from the buffer during dissembly and storage of the halfed lower.
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