Help matching upper with my lower...

[6point7Cummins]

Hello all, I purchased a built .308 upper, used, several years back (mistake No. 1).  I then had a local FFL who claimed to be a manufacturer, who apparently knew nothing about .308s, build my lower (mistake No. 2). The weapon had a serious malfunction basically rendering the upper a hunk of garbage. Oh well...the builder reimbursed me for the money spent on the upper.

Now I am ready to purchase an upper, from a reputable manufacturer. My question is, how do I know how to properly match an upper to my lower?  The builder does not recall which parts he used, LR308 vs. Armalite. He "thought" Ar-10. Is it really crucial that the lower parts type match the upper or more crucial the upper is made from all matching parts?

ive included some pictures of my lower.  The last picture shows damage to buffer tube threads (only damage sustained to the lower). The buffer still threads just fine.

Thanks for any help you guys can offer...

.

 

[jtallen83]

As much as it pains me I would say buy a CMMG upper. That is a DPMS LR308 pattern, not an AR-10. There are different generations of CMMG, somebody here should be able to tell you what to look for.

And welcome to the forum!

Edited July 8, 2017 by jtallen83

[6point7Cummins]

Thank you!

Why does it "pain" you if you don't mind me asking?  I was looking at uppers build by Ground Zero Precision. I think they use Aero Precision uppers...

https://www.groundzeroprecision.com/collections/ar-10-lr-308-ar-large-bore-variant-upper-receivers/products/custom-ultra-match-ballistic-advantage-aero-precision-6-5-creedmoor-ar-upper-receiver-complete

Edited July 8, 2017 by 6point7Cummins

[jtallen83]

Do some searching here on CMMG. They have had some questionable QC at times. That said there are some that have no problem.

[survivalshop]

  I would say to purchase a CMMG Upper also , just because of the possibility of Tolerance stacking issues . I had an early CMMG Lower that I put an SI Defense Gen. II Billet Upper Receiver on & the rifle functioned with any Metal Mag , but the first Gen. LR Mags , just would not work . Not to mention the fitment was on the loose side , even for me . 

 When Magpul came out with the Gen 3 LR Mags , they worked as did Lancer L7"s 308 Mags , but I'm not sure if it was because of the changes that Magpul did to the Gen 3's or all the shimming & bedding I did to tighten up the Receivers . The Rifle worked fine when I sold it to a friend & he loves it . 

   You can try any DPMS type Upper , but these aren't like the Milspec little brothers , sometimes its a crap shoot . We like to alway recommend the same manufacturers Upper & lower Receivers so as not to have any issues with Tolerance stacking .

 You Lower Receivers Extension Threads look like your BCG hit it , threads look OK to be able to install another Receiver Extension with out issue . Probably because of wrong or mismatched Buffer Components .

Edited July 8, 2017 by survivalshop

[6point7Cummins]

Thanks Survival Shop. How can I know if I have correct buffer and spring?  Should I just buy another?  Is there something specific I should look for when buying one?

[98Z5V]

1 hour ago, 6point7Cummins said:

Thanks Survival Shop. How can I know if I have correct buffer and spring?  Should I just buy another?  Is there something specific I should look for when buying one?

Measurements, measurements, measurements...  That's what it comes down to with these things.  Buffer lengths (both carbine are rifle) are different than AR15 parts.  Buffer springs are different than AR15 parts, in both relaxed length, coil count, and wire diameter. 

Rifle receiver extensions are all the same. There is zero difference in a rifle receiver extension, in construction, even though you'll find "A1 and A2" extensions.  An A2 extension is nothing more than a 5/8" spacer on the end of an A1 extension, with a longer vented screw (upper screw).  Well, and the longer A2 stock that covers it all.  Rifle receiver extensions are all the same - extra parts for the A2 stuff to make it 5/8" longer in the stock body.

Carbine receiver extensions have two flavors - standard AR15 carbine receiver extensions fit on 308s.  They just use a 308AR shortass carbine buffer and a different spring (than an AR15).  This is because the bolt carrier is longer in a 308. Shorter buffer, longer bolt carrier, has to fit into the same space...  AR15 carbine receiver extensions have an internal depth of 7.000".

Armalite went about it different in the AR-10 Carbine - they made a longer AR-10 Carbine receiver extension, and the internal depth on that is 7 5/8".  It uses the Armalite EA1095 buffer spring (same spring for both rifle and carbine recoil systems in the AR-10, the EA1095).  It uses standard AR15-lengthed carbine buffers, in the H3 weight.  This is a better carbine recoil system for 308ARs.

Here's the tech data on recoil systems - spring lengths, coil counts, wire diameters, buffer lengths...  this is THE authority on recoil systems...

http://heavybuffers.com/reference.html

Edited July 10, 2017 by 98Z5V

[6point7Cummins]

98Z5V, great info. Much appreciated. I'm guessing since this is a LR308 based lower, I'd be dealing with the carbine setups, shorter buffer like you said in a standard extension?  I'll check the lengths on my buffer and spring. I have a feeling they are wrong. 

[98Z5V]

You can run the Armalite AR-10 Carbine recoil system on a DPMS-based 308.  I'm doing it on 3 of them. 

[survivalshop]

 

12 hours ago, 98Z5V said:

This is a better carbine recoil system for 308ARs.

 There's only around a  bazillion DPMS based Carbine Buffer systems out there working fine , so saying one is better then the other , mote .

[unforgiven]

2 hours ago, survivalshop said:

 

 There's only around a  bazillion DPMS based Carbine Buffer systems out there working fine , so saying one is better then the other , mote .

Hey bro how many zero's are in a bazillion   

[survivalshop]

3 hours ago, unforgiven said:

Hey bro how many zero's are in a bazillion   

?      

[98Z5V]

7 hours ago, survivalshop said:

 

 There's only around a  bazillion DPMS based Carbine Buffer systems out there working fine , so saying one is better then the other , mote .

On that note, there's that many manufacturers that think they can get it right - and they don't always.  Wrong buffer spring, buffer that's 0.050" too long, receiver extension that 0.100" too deep...  and your recoil system is jacked and not working right.

There's only one manufacturer for the parts I listed, and I've never heard of them getting it wrong on that recoil system.  I'm just sayin'... 

[survivalshop]

2 hours ago, 98Z5V said:

On that note, there's that many manufacturers that think they can get it right - and they don't always.  Wrong buffer spring, buffer that's 0.050" too long, receiver extension that 0.100" too deep...  and your recoil system is jacked and not working right.

There's only one manufacturer for the parts I listed, and I've never heard of them getting it wrong on that recoil system.  I'm just sayin'... 

 Doesn't change that Bazillion number that work .

[6point7Cummins]

On 7/9/2017 at 7:00 PM, 98Z5V said:

Measurements, measurements, measurements...  That's what it comes down to with these things.  Buffer lengths (both carbine are rifle) are different than AR15 parts.  Buffer springs are different than AR15 parts, in both relaxed length, coil count, and wire diameter. 

Rifle receiver extensions are all the same. There is zero difference in a rifle receiver extension, in construction, even though you'll find "A1 and A2" extensions.  An A2 extension is nothing more than a 5/8" spacer on the end of an A1 extension, with a longer vented screw (upper screw).  Well, and the longer A2 stock that covers it all.  Rifle receiver extensions are all the same - extra parts for the A2 stuff to make it 5/8" longer in the stock body.

Carbine receiver extensions have two flavors - standard AR15 carbine receiver extensions fit on 308s.  They just use a 308AR shortass carbine buffer and a different spring (than an AR15).  This is because the bolt carrier is longer in a 308. Shorter buffer, longer bolt carrier, has to fit into the same space...  AR15 carbine receiver extensions have an internal depth of 7.000".

Armalite went about it different in the AR-10 Carbine - they made a longer AR-10 Carbine receiver extension, and the internal depth on that is 7 5/8".  It uses the Armalite EA1095 buffer spring (same spring for both rifle and carbine recoil systems in the AR-10, the EA1095).  It uses standard AR15-lengthed carbine buffers, in the H3 weight.  This is a better carbine recoil system for 308ARs.

Here's the tech data on recoil systems - spring lengths, coil counts, wire diameters, buffer lengths...  this is THE authority on recoil systems...

http://heavybuffers.com/reference.html

I looked at that chart and I'm lost. How do you know which one you need. There aren't any measurements. 

 

My extension tube is 9 5/8" deep. Here a pic

[6point7Cummins]

Okay, correct me if I am wrong, but this buffer and spring combo appears to be carbine length...looks like the right buffer for a .308 also. I just need to make sure I get a carbine length gas system on my upper, right?

 

[survivalshop]

25 minutes ago, 6point7Cummins said:

Okay, correct me if I am wrong, but this buffer and spring combo appears to be carbine length...looks like the right buffer for a .308 also. I just need to make sure I get a carbine length gas system on my upper, right?

 

Are you using that stock & Receiver Extension ?  Not sure what that Stock uses ,  Because that is a Rifle Length Receiver Extension & appears it is a Carbine length Buffer & Spring . DPMS systems ,have to have 308 Rifle components with Rifle components & 308 Carbine components with 308 Carbine components , can't miss match the two . Armalite AR 10 components use a different system , as was noted by 98 . 

.Gas system has little to do with Buffer system , but saying that , you can tune a rifles recoil impulse somewhat with a Heavy Buffer & there are different weight Buffer Springs out there now a days to aid function  , but std ( Rifle /Carbine ) Springs work .

[98Z5V]

3 hours ago, 6point7Cummins said:

I looked at that chart and I'm lost. How do you know which one you need. There aren't any measurements. 

 

My extension tube is 9 5/8" deep. Here a pic

That a 39-coil spring, and it looks to be just short of 11", so that's an AR15 Carbine spring, and a weak one at that, because it's relaxed length should be 11.25" long.  Could be camera angle, but that spring isn't 11.25" long - doesn't matter, because that spring will have your BCG body slamming into the back of your upper receiver.

The buffer looks like a DPMS-based LR308 carbine buffer - looks like it's 2.5" long.

Okay, so that's a mix-match of Carbine recoil system parts (308 in one, AR15 the other), but attempting to run a 308 gun in a rifle-length receiver extension.

That will jack your lower receiver all up, possibly with permanent damage to it, just from firing it like that.

That A1 rifle-length receiver extension is okay with that stock - you might want to check and see if that stock needs the "A2-length" recoil system.  If it does, you need the 5/8" spacer for it, and the longer vented screw.

Next, you need a DPMS-based LR308 rifle buffer, and it should be 5.200" long.  If you get a rifle buffer that's for an AR15, it will be 5.900" long, and it won't work in your 308 - it will be short-stroking, because the BCG can't travel far enough.  So, LR308 OR AR-10 rifle buffer is needed - they're both 5.200" long.

Next, you need a DPMS-based LR308 Rifle buffer spring, OR the AR-10 Rifle buffer spring.  Both will work in that rifle receiver extension.  If it's an AR-10 rifle buffer spring, then it's gonna have the relaxed length of 13.75", have 34 coils, and the wire diameter is gonna be 0.072".  Armalite uses the exact same spring in the AR-10 rifles and AR-10 Carbines.  It's got an Armalite part number of EA1095. 

If your stock body requires the "A2 length," then you need these two additional parts, right here:

Edited July 11, 2017 by 98Z5V

[98Z5V]

^^^  That right there, SS?...     THAT is the reason that the AR-10 Carbine recoil system is superior in a 308AR, if you plan on running a collapsible stock.  You know why, brother?  Vendors can't fuk it up.  You order (real) AR-10 parts, and you get REAL AR-10 parts, that just work.  For that reason only, it's far superior in a large frame AR carbine recoil system.  

[DNP]

Gawd dammit R2.....what did you slip into that last batch of koolaid!!?

 

I'm not sayin anything good or bad....it just smells funny. 

[98Z5V]

By the way, there's a Metric Shiit-Ton of measurement data in this table. I'm just sayin'...

My Metric Shiit-Ton exactly equates to SS's Bazillion.  Plus 1.   

Click it, and it get's bigger...  

 

 

 

 

 

Edited July 11, 2017 by 98Z5V

[6point7Cummins]

8 hours ago, 98Z5V said:

That a 39-coil spring, and it looks to be just short of 11", so that's an AR15 Carbine spring, and a weak one at that, because it's relaxed length should be 11.25" long.  Could be camera angle, but that spring isn't 11.25" long - doesn't matter, because that spring will have your BCG body slamming into the back of your upper receiver.

The buffer looks like a DPMS-based LR308 carbine buffer - looks like it's 2.5" long.

Okay, so that's a mix-match of Carbine recoil system parts (308 in one, AR15 the other), but attempting to run a 308 gun in a rifle-length receiver extension.

That will jack your lower receiver all up, possibly with permanent damage to it, just from firing it like that.

That A1 rifle-length receiver extension is okay with that stock - you might want to check and see if that stock needs the "A2-length" recoil system.  If it does, you need the 5/8" spacer for it, and the longer vented screw.

Next, you need a DPMS-based LR308 rifle buffer, and it should be 5.200" long.  If you get a rifle buffer that's for an AR15, it will be 5.900" long, and it won't work in your 308 - it will be short-stroking, because the BCG can't travel far enough.  So, LR308 OR AR-10 rifle buffer is needed - they're both 5.200" long.

Next, you need a DPMS-based LR308 Rifle buffer spring, OR the AR-10 Rifle buffer spring.  Both will work in that rifle receiver extension.  If it's an AR-10 rifle buffer spring, then it's gonna have the relaxed length of 13.75", have 34 coils, and the wire diameter is gonna be 0.072".  Armalite uses the exact same spring in the AR-10 rifles and AR-10 Carbines.  It's got an Armalite part number of EA1095. 

If your stock body requires the "A2 length," then you need these two additional parts, right here:

Sounds like the guy that put all this together really knew what he was doing...

I'm gonna call Luth and see which extension it needs then order the correct buffer/spring. Thanks for the help. 

What I got also from these responses, the gas system length won't matter when purchasing the upper?  Or do I need to make sure its rifle length to match recoil system?

[6point7Cummins]

8 hours ago, 98Z5V said:

By the way, there's a Metric Shiit-Ton of measurement data in this table. I'm just sayin'...

My Metric Shiit-Ton exactly equates to SS's Bazillion.  Plus 1.   

Click it, and it get's bigger...  

 

 

 

 

 

Yeah, I was looking just at the DPMS .308 section. I see it now. I'm retarded. 

[edgecrusher]

Gas system has no effect on buffer type/systems, correct. Most shooters tend to find a longer gas impulse has less recoil

[survivalshop]

9 hours ago, 98Z5V said:

^^^  That right there, SS?...     THAT is the reason that the AR-10 Carbine recoil system is superior in a 308AR, if you plan on running a collapsible stock.  You know why, brother?  Vendors can't fuk it up.  You order (real) AR-10 parts, and you get REAL AR-10 parts, that just work.  For that reason only, it's far superior in a large frame AR carbine recoil system.  

      Ya mostly because they make them & only them ( or from a outside vender ), so how many venders out there make or sell DPMS based systems , Bazillions , thats how many . If I make or sell  5 springs a year compared to someone else who makes five thousand & from various manufacturers of springs , with venders asking for different spec's to use in their proprietary rifles , who has a better chance of having a out of spec spring for a DPMS Based system ? Because some idiot manufacturer makes a Spring for their proprietary rifle & someone uses it in a std DPMS based rifle , how you going to blame the DPMS system ? Or better yet , someone who uses an AR 15 Spring or Buffer in a 308AR , we going to blame that on the DPMS based system for 308AR ?

   I have ordered many springs made for or from DPMS & all of them were correct & worked fine . I can tell you , if others made Armalite AR 10 Springs & sold them , you would get an occasional bad one . Thing is, there is not the demand for them as is for the DPMS based system . Doesn't meant one is better then the other .

   Nothing wrong with ether system, if correct components used  , but their are a Bazillion more DPMS based rifles out there that work fine ,then the AR 10 , period . 

  We can thank Mr. Stoner for both rifle systems , so it really doesn't matter what the words say on the Receiver .

  

Edited July 11, 2017 by survivalshop