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[ARCHIVED THREAD] - AR 308: Has this ever happened to you? ** Now with AAR... **

Posted: 6/25/2017 8:17:22 PM EDT

Doing a bit of routine maintenance and found this...

The lil' pin on the buffer retainer was being bent forward. First time I've ever seen this. And on a low round count gun, no less.

Any guesses as to the cause?

Posted: 6/25/2017 9:45:45 PM EDT

[#1]

Chi-com pot metal?

Posted: 6/25/2017 9:50:32 PM EDT

[#2]

Lower not in spec.

Recoil spring strength is shoving the buffer and BCG back into battery as it should.

Buffer retainer is placed too far to the rear, so it's taking a beating.

Posted: 6/25/2017 11:02:27 PM EDT

[#3]

Quote History

Quoted:

Buffer retainer is placed to far to the rear, so it's taking a beating.

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This would be my first guess, as well. If the retainer hole is placed too far back, it causes the BCG to not push the buffer far enough back upon closing (upper/lower), which in turn means every shot hammers the buffer into the retainer (normally they do not contact unless top receiver is removed, the sole purpose of the retainer is to retain the buffer WHEN NOT ASSEMBLED/or open).
Slowly close the upper and see if the BCG appears to push the buffer back. If not, that's your problem.

Posted: 6/25/2017 11:28:05 PM EDT

[#4]

Quote History

Quoted:

This would be my first guess, as well. If the retainer hole is placed too far back, it causes the BCG to not push the buffer far enough back upon closing (upper/lower), which in turn means every shot hammers the buffer into the retainer (normally they do not contact unless top receiver is removed, the sole purpose of the retainer is to retain the buffer WHEN NOT ASSEMBLED/or open).
Slowly close the upper and see if the BCG appears to push the buffer back. If not, that's your problem.

View Quote

Also what does the buffer look like. I've seen when the lower is not spec and the buffer retainer is damaging the buffer.

this is what should fix the issue

Posted: 6/27/2017 5:52:07 PM EDT

[#5]

Quote History

Quoted:

This would be my first guess, as well. If the retainer hole is placed too far back, it causes the BCG to not push the buffer far enough back upon closing (upper/lower), which in turn means every shot hammers the buffer into the retainer (normally they do not contact unless top receiver is removed, the sole purpose of the retainer is to retain the buffer WHEN NOT ASSEMBLED/or open).
Slowly close the upper and see if the BCG appears to push the buffer back. If not, that's your problem.

View Quote

Thanks for the info!

I just looked at the lower/upper and it appears the BCG IS pushing the buffer back a bit. However... I'll bet it's not enough.

My guess is that since it's only he lower edge of the BCG that pushes the buffer back, after the upper is completely lowered and pinned, the buffer comes back forward the same distance to rest back on the retainer pin.

The buffer (XH CAR-10 from Slash) still looks good with only a couple small marks on the edge.

I'm going to get in touch with the manufacturer and see what they'll do for me. In the mean time, I'm going to give that offset pin retainer a try.

Thanks again for the help!!!

Posted: 6/27/2017 10:19:04 PM EDT

[#6]

There should be no marks on the edge of the buffer if everything is on spec.

Lower is out, plus a cheap retainer pin that has bent so easily. Proper pin would last longer and chew up the buffer quite a bit before snapping.

Posted: 6/27/2017 11:01:00 PM EDT

[#7]

from the pic, you seem fine

pin is soft metal or the chinese crap was made very poorly

Posted: 6/28/2017 1:16:36 AM EDT

[#8]

if you aren't using an adjustable gas block or heavy buffer and spring. the 308 rocks the bolt back hard, you can even get receiver damage

Posted: 6/28/2017 9:41:41 AM EDT

[#9]

Given that there is no official "spec" for .308 ARs, I would call it an "incompatibility" between the lower and the bolt carrier . . .

Posted: 6/28/2017 4:12:32 PM EDT

[#10]

Quote History

Quoted:
if you aren't using an adjustable gas block or heavy buffer and spring. the 308 rocks the bolt back hard, you can even get receiver damage

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I'm using a XH CAR-10 buffer from Slash and is spring. Also, I'm trying out a adjustable gas key (RCA I believe) on the bolt carrier.

Posted: 6/28/2017 4:14:34 PM EDT

[#11]

Quote History

Quoted:
Given that there is no official "spec" for .308 ARs, I would call it an "incompatibility" between the lower and the bolt carrier . . .

View Quote

Upper, lower and BCG are all from the same manufacturer. I guess a incompatibility is still possible...

Posted: 6/28/2017 4:17:28 PM EDT

[#12]

It was mentioned to me to try a JP silent captured spring. Then I could eliminate the buffer retainer all together.

Your thoughts?

Posted: 6/28/2017 4:19:08 PM EDT

[#13]

Quote History

Quoted:
this is what should fix the issue

https://s3.amazonaws.com/mgm-content/sites/armslist/uploads/posts/2016/07/07/5653918_04_buffer_retainer_pin_offset_ar1_640.jpg

View Quote

This is your ultimate fix, offset retainer.
Unless you want to try replacing major components and hoping you don't end up with the same result.

Posted: 7/2/2017 11:00:53 PM EDT

[#14]

By all means correct me if I'm wrong. But doesn't the buffer tube slightly engage the buffer retainer, to keep it from launching out during cycling. Or maybe that's only on carbine length buffer tubes. I'm not an expert but my rifles buffer tube engages the lip edge of the buffer retainer, to keep it in position. Judging by the picture, the buffer tube is not far enough into the receiver to engage the buffer retainer.

Posted: 7/2/2017 11:12:21 PM EDT

[#15]

Sorry it's hard to tell, hard to get a good picture while holding the buffer back. This is a rifle length buffer tube. And the buffer tube does indeed engage the lip edge of the buffer retainer to hold it in position. My guess is the buffer tube on your rifle is a thread or so loose allowing for enough gap for the retainer to get farther up than it should during operation causing recoil damage.

Attached File

Posted: 7/3/2017 9:52:10 PM EDT

[#16]

AAR:

I took delivery of the retainer with the offset pin. The order went through without issue. Comms were great and the retainer showed up in 3 days. Insallation was typical of a standard mil-spec part with the exception of making sure the receiver extension "lip" engaged the register on the retainer.

For comparison...

This is the original set up with a mil-spec buffer retainer.

Here's the same shot with the offset pin retainer installed.

With the new retainer installed, I gained an extra .030" (+/-) of clearance between the pin and buffer face! Obviously I couldn't measure it with the rifle all pinned up. But we were able to get precision drill bits in between the buffer and pin.

Bench and backyard testing went well with buffer having ZERO contact with the pin. I'm cautiously optimistic that the issue has been resolved.

Side note... The manufacturer has yet to respond to my emails. My guess is it's going to be like pulling teeth to get their attention. I'm good with my current set up. BUT... The lower IS out of spec and should be replaced. I do believe their phone will be ringing come Wednesday.

Posted: 7/4/2017 1:46:59 AM EDT

[#17]

IDK, your first pic looks like proper buffer protrusion to me (second pic looks WAY far forward). Was the buffer getting chewed up? If not, it may have just been a poorly made retainer (original one). That offset setup does not look right at all. Just my .02

Posted: 7/4/2017 3:54:04 AM EDT

[#18]

Buffer tube could be out of spec too. They don't all have the same lip, and are not all threaded equally and are not always the same length. We're talking thousandths here, but differences all the same.

Maybe tolerance stacking is the problem. Everything is within their margin of error to be an "in spec" part for the mfg, but together just eats itself up.

Posted: 7/4/2017 4:44:54 AM EDT

[#19]

Quote History

Quoted:
IDK, your first pic looks like proper buffer protrusion to me (second pic looks WAY far forward). Was the buffer getting chewed up? If not, it may have just been a poorly made retainer (original one). That offset setup does not look right at all. Just my .02

View Quote

I thought the original protrusion was GTG as well. No buffer damage but a very bent pin on the original retainer.

It may be the original retainer was poorly made. BUT... The buffer should not have been in contact with it IF the retainer hole in the lower was in spec. The buffer retainer is only a convenience... Its there only hold the buffer in the receiver extension during assembly/disassembly. I could pull the retainer completely and be GTG. But the takedown / assembly would be a PITA... I tried it... Not fun but do-able.

By my read, the greater the distance between the pin and buffer... All the better. I can close the upper down on the lower, pin them together, rack the action, and fire a few rounds. A long term range session is in order...

Posted: 7/4/2017 5:01:05 AM EDT

[#20]

Quote History

Quoted:
Buffer tube could be out of spec too. They don't all have the same lip, and are not all threaded equally and are not always the same length. We're talking thousandths here, but differences all the same.

Maybe tolerance stacking is the problem. Everything is within their margin of error to be an "in spec" part for the mfg, but together just eats itself up.

View Quote

AGREED!! The buffer tube is Magpul from a UBR gen 1 kit. That said, and from my personal experience, Magpul is GTG. However... With the the "standard" UBR buffer tube (which a 308 AR standard doesn't exist) and the lower held to the same NON standards... Stacking is very much a possibility.

How do you call "out of spec" if there really isn't any? My read is that if all "specs" were GTG, the buffer retainer would NOT have been bent forward as shown in my OP.

I have a solution that works. However, I feel it should not have come to me throwing more parts at a problem that should have been resolved before production. Yet with NO 308AR specs... What do ya do? The manufacturer used that line on me with a different issue!

HARD range session to follow to provide proof of function... Or not....

Posted: 7/4/2017 2:26:01 PM EDT

[#21]

Each manufacturer has their own spec for a variety of AR-10 style rifles. An actual manufacturing company saying to a customer "their is no spec" is a very lazy non-answer to give a customer.

I know on my WW SRC 308, a number of parts are actually AR-15 standard. While others are obviously unique to their specifications on their SRC-308. Their is a spec, but not a standard for manufacturing AR-10s that is adhered to by these companies. KAC, DPMS, Bushmaster, Armalite, etc... They all follow a specification when building their guns.

However their was never a US 'mil spec' AR-10, so hence everyone keeps on the 'no spec' bandwagon. This is especially annoying for an actual manufacturer to say. I think it's poor customer service and pure laziness.

"Sorry to hear about that, we can't help you though. Their is no spec on our products so good luck reverse engineering our bazaar design..."

Posted: 7/4/2017 2:45:57 PM EDT

[#22]

Maybe the bcg is to short?

Posted: 7/4/2017 6:01:52 PM EDT

[#23]

Quote History

Quoted:
Maybe the bcg is to short?

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We did think of that. We measured that same "buffer to pin" distance I mentioned earlier, using (4) BCGs from (3) different manufacturers. Aero Precision, Young N/M and RCA (I believe). All were within a couple thou +/-.

I'm about to conclude this issue is a case of tolerance stacking. I would still like the manufacturer to take a look at it. Maybe they had a bad run. Who knows.

Posted: 7/4/2017 7:30:35 PM EDT

[#24]

i was thinking "bolt carrier too short" also, but since you measured it, i guess not.

for the sake of argument, assume the buffer retainer pin location is within spec.

then, the symptom is that the BCG is at rest too far forward. and the BCG rests against the barrel extension. so, is the barrel extension too far forward? on some handguards, the installation kit includes some shims that are kinda thick-ish in my opinion, those would move the barrel extension forward in the receiver, so the BCG is then more forward. is that what was used in this case?

or in that same vein, the front face of the upper receiver is out of spec and a little too long, resulting in too much length between the buffer face and the barrel extension.

i'm guessing something is off by 10 or 20 thousandths, that range.

grasping at straws.

Posted: 7/4/2017 7:38:56 PM EDT

[#25]

Quote History

Quoted:
It was mentioned to me to try a JP silent captured spring. Then I could eliminate the buffer retainer all together.

Your thoughts?

View Quote

It would in fact eliminate the need for it all together. I have never used the JP for the AR10 but I do have one on my AR9mm...it works great.

Posted: 7/4/2017 10:00:11 PM EDT

[#26]

Quote History

Quoted:
i was thinking "bolt carrier too short" also, but since you measured it, i guess not.

for the sake of argument, assume the buffer retainer pin location is within spec.

then, the symptom is that the BCG is at rest too far forward. and the BCG rests against the barrel extension. so, is the barrel extension too far forward? on some handguards, the installation kit includes some shims that are kinda thick-ish in my opinion, those would move the barrel extension forward in the receiver, so the BCG is then more forward. is that what was used in this case?

or in that same vein, the front face of the upper receiver is out of spec and a little too long, resulting in too much length between the buffer face and the barrel extension.

i'm guessing something is off by 10 or 20 thousandths, that range.

grasping at straws.

View Quote

The barrel is Fulton Armory. Without braking the bank, it was the only 18"ish 308 barrel I could find at the time with a rile length gas system. The handguard is PRI... No shims were needed for either the barrel or handguard.

I did not square off the face or the upper receiver. Hmm... That's an interesting possibility. Maybe I should break out the 4 jaw and make a few... very few... chips. Could'nt hurt, right?

Posted: 7/5/2017 7:19:35 AM EDT

[#27]

Quote History

Quoted:
grasping at straws.

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Yeahhh, most likely culprit is the buffer retainer hole, it's a different setup than the rest and I've seen several receivers over the years with it slightly out of location...

Posted: 7/5/2017 3:59:53 PM EDT

[#28]

Quote History

Quoted:

Yeahhh, most likely culprit is the buffer retainer hole, it's a different setup than the rest and I've seen several receivers over the years with it slightly out of location...

View Quote

Exactly. Even my MEGA MATEN required attention at this location. I handled it by cutting a shoulder out of the buffer and let it ride over the top of the retainer pin, but either way works.