80% build/buffer tube question.

[Vermonter]

Howdy folks. I'm new to the world of working with AR platform rifles. I have built several AR 15's with various 80 percent lowers with no real problems so far. I decided to work on a DPMS pattern LR 308 build using a forged 80% lower from Rightobear.

My question is this. I purchased a complete upper from Bear Creek Arsenal with a 16 inch barrel along with a basic A2 stock kit from UTG. I've used the A2 style stock kit from UTG on a AR 15 build I did with very good luck, and was happy with the results.

When I assembled the rifle, the buffer tube shoulders out and tightens well before the lip of the buffer tube has a chance to catch and retain the detent pin. If I simply remove the detent and spring, with a bit of patience I can retain the spring and buffer, simply close the upper and lower and all seems well. I have not attempted to fire the rifle yet, from what I can tell every function seems fine, the magazine seems fine, the bolt catch seems to function fine, and all features of the BCG appear to be A-Ok. Am I missing something? Am I making some kind of rookie error?

From what I've been told and researched the .308 builds can be a bit more fussy thank working with the AR-15, is that a correct thought?

Thank you in advance for input!

[jtallen83]

Is the hole in the lower for the detent and spring drilled at an angle towards the tube or straight up and down? I don't know crap about the 80% stuff but people that know machining have discussed that issue here in the past. Pictures are a must for this kind of thing, show us what you got.

[Vermonter]

[Vermonter]

Okay. Here are a couple of pictures. From looking at it I'd say the bore for the detent is at a slight angle. 

[unforgiven]

17 minutes ago, Vermonter said:

Okay. Here are a couple of pictures. From looking at it I'd say the bore for the detent is at a slight angle. 

That's an understatement brother all pins are perpendicular to the body of the receiver. That's what I have anyway. Just my 2 mags

 

[jtallen83]

5 hours ago, Vermonter said:

he buffer tube shoulders out and tightens well before the lip of the buffer tube has a chance to catch and retain the detent pin

So the tube is as far as it goes in those pics? Do you have another buffer tube you could check? Doubt it's the tube though, sure looks like some dimensional issues there.

[Vermonter]

2 hours ago, jtallen83 said:

So the tube is as far as it goes in those pics? Do you have another buffer tube you could check? Doubt it's the tube though, sure looks like some dimensional issues there.

Correct. The design of the UTG buffer tube is a machined shoulder. According to the instructions you torqe the tube to spec and you're done if memory serves me correctly. I do have other buffer tubes that I can try. In the next few days if time permits I'll see how other ones fit.

As a note I actually called the Leapers/UTG customer service line and spoke with a rep. To the best of the knowledge of the guy I talked to, and the person he confered with they aren't aware of other people experencing the same problem.

[98Z5V]

On 2/25/2022 at 8:49 AM, Vermonter said:

Okay. Here are a couple of pictures. From looking at it I'd say the bore for the detent is at a slight angle. 

Should be a 6* angle, exactly.  That's the spec for it.

[98Z5V]

On 2/25/2022 at 6:48 AM, Vermonter said:

with a basic A2 stock kit from UTG.

1 of 2 things going on here, since you're using a rifle recoil system (complete).  

1.  That UTG rifle receiver extension is out of spec, because it doesn't come forward enough - even fully threaded into the lower receiver - to even GET to the buffer retainer pin. 

2.  That 80% lower is out of spec, and is too deep in the backend, and NOTHING will thread into that thing to capture that buffer retainer pin.

It can only be those 2 things, nothing more.  Start measuring, and comparing specs.

Edited March 1, 2022 by 98Z5V

[Vermonter]

On 3/1/2022 at 12:01 AM, 98Z5V said:

1 of 2 things going on here, since you're using a rifle recoil system (complete).  

1.  That UTG rifle receiver extension is out of spec, because it doesn't come forward enough - even fully threaded into the lower receiver - to even GET to the buffer retainer pin. 

2.  That 80% lower is out of spec, and is too deep in the backend, and NOTHING will thread into that thing to capture that buffer retainer pin.

It can only be those 2 things, nothing more.  Start measuring, and comparing specs.

 

Thank for your reply!

After trying the buffer tube on other rifles and taking some measurements the problem does indeed look like the lower is out of spec. I reached out to the vendor, and interestingly enough they say the manufacturer is no longer producing them, even though I bought these about two months ago. They have offered me a full refund, and are working to make things right. I asked if this was a known quality issue, and am awaiting a response to that answer. I have also asked if they offer any other 80 percent lowers in .308 to simply swap them out. Again, I'm awaiting an answer. I'll pass along more information as I have it.

[98Z5V]

7 hours ago, Vermonter said:

 

Thank for your reply!

After trying the buffer tube on other rifles and taking some measurements the problem does indeed look like the lower is out of spec. I reached out to the vendor, and interestingly enough they say the manufacturer is no longer producing them, even though I bought these about two months ago. They have offered me a full refund, and are working to make things right. I asked if this was a known quality issue, and am awaiting a response to that answer. I have also asked if they offer any other 80 percent lowers in .308 to simply swap them out. Again, I'm awaiting an answer. I'll pass along more information as I have it.

This is fixable, since it's an 80%...   Thread the extension back into the lower, determine how short it is, to make the end of the extension cover the edge of the retainer when it's in there, and machine that much off the flat back edge of the lower receiver.  Another way is this:  that receiver extension should be 9 11/16" deep, internally.  You want the forward edge of that extension to stop right at the top of the lower receiver.  Measure what it is now, fully threaded in, from the internal back of that extension to the top edge of the lower.  Machine off enough (off the back of that receiver) to get to 9 11/16" for that measurement.  

Either one of those two methods will solve the problem.  You're already machining anyway, just go for it.  

[Patrad]

Howdy Vermonter. As an FYI, I just finished my 1st AR308 build. My lower is also an 80%, but made by 80% Arms - https://www.80percentarms.com/products/black-anodized-billet-308-80-lower-receiver/

My buffer assembly is an Aero, also from 80%Arms - https://www.80percentarms.com/products/complete-308-ar-10-buffer-tube-kit/ . BTW, the buffer is a 3.8oz buffer.

I also use their Gen 3 Multi Platform Jig - https://www.80percentarms.com/products/easy-jig-gen-3-multi-platform-ar-15-ar-9-and-308-80-lower-jig/ . Again, NEVER a problem.

NO problems whatsoever. I've also built several AR15's as well. All I've ever used is 80% Arms lowers - NEVER had any problems with any of then, either. They also have many other goodies, too. Great customer service, too!

For this build, I used a BCA 20" SS straight fluted, rifle length gas upper - https://www.bearcreekarsenal.com/calibers/308-winchester/308-complete-uppers/308-20-ss-mid-weight-barrel-1-10-twist-rifle-15-handguard-rc-sp-nrail-spiral-flash.html. Flash hider might vary, depending on stock supply. Hope this is of some help.

Patrad.

PS: Yes, I know the scope is at an angle - it's only there for the pic.😉