"DPMS style .308 AR10" Failure to Feed Issue

[CentralNChunter]

Before someone goes to correct me that only Armalite is AR 10, the title " DPMS style .308 AR10" is a copy and paste from Thunder Guns LLC were this 80% was purchased.  Mine is a DPMS "High" pattern.  https://www.thundergunsar.com/ar10-receivers/upper-receivers/

The issue I am having: When the bolt pushes a round from the magazine, as the bullet starts up the feed ramp the bolt slips over the case head and jams (bolt over brass).  I think it's mostly, if not completely happening when the round being feed from the magazine is on the RH side of the mag.  Magazines tried: PMAG M3 20rd, Lancer L7AWM 20rd.  From the spec's on this drawing: https://www.thundergunsar.com/ar10-receivers/upper-receivers/    The location of the mag catch cut in the lower is the exact distance down from the top of the lower and height as shown on print. Someone on the Practical Machinist forum posted his DPMS bolt (dia over opposing lugs) .891" which is what mine measured.  From spec's I can find my parts seem to be in spec. With the mag catch pushed in, the PMAG can be inserted 0.053" deeper and the L7 0.063" deeper.  If nobody has any other solution (besides modified mags as I want the ability to use off the shelf unmodified mags), I have the idea of cutting the mag catch slot 0.045"-0.050" higher and making a new mag catch.  This would move the magazine up enough to solve my issue.  I think.  Is there a solution I'm not seeing?

Billy

Parts: Thunder Guns 308 DPMS style 80%upper/lower, BCM charging handle, AIM AR 308 BCG, PMAG, Lancer L7, barrel made from Begerra blank & BAT Machine barrel extension.

[98Z5V]

Thunder Guns LLC just came up recently in conversation.  Please read this thread - I know it doesn't help you now, but you'll know what you're looking at for trying to resolve this issue.

If it's compound problems, from cheap, out-of-spec components, I'm not sure there's much that we can do to help you resolve this.

EDIT - your own machining solution might be the only possible solution.  It sounds like it would work...

Edited May 23, 2017 by 98Z5V

[survivalshop]

 Can we see a photo of the Feed ramps in the Upper receiver/Barrel Extension ?  

 I have measurements of different heights of Cases in the mag in relation to the deck flat of the Lower Receiver . I had an issue similar to this with a CMMG Lower . An Armalite AR 10  , ( I believe the AR 10A ) Mag Catch may help & may be worth a try. Basically it the height above the Deck of the Lower Receiver , that aligns the Cartridges to be fed at the proper height  , from the Mag..  

 I will look up my notes. As long as the Mag Catch is cut into the Receiver , in relation to that top deck of the Lower Receiver , it should work .

 Also , How much play is there in the Back of the Receivers , where the meet or Disassembly Pin play ? 

[Robocop1051]

Have you tried a different bolt yet? Your AIM bolt may be out of spec, just enough to make a difference. This could be an issue of tolerance stacking. 

[CentralNChunter]

I have not tried a different bolt. I have a friend that owns a PSA & another that has DPMS but would be unable to get up with either until the 2nd Sat next month.  Per the dimensions found online from another guys DPMS bolt, mine is the exact same diameter, which I believe would be the measurement that matters for this issue. 

98Z5V , if you have DPMS pattern print specs that is different than what I have came up with, I would be glad to accept a copy to compare to my parts. Sounds like I didn't use the brand or retailer you are partial to. From what I found on the web, my parts are in spec for DPMS pattern, but as you stated in another post, 308AR is not standardized & companies can make whatever they want.

Survivalshop, I'm at work now but will reply to your questions as soon as I'm able.

[mrmackc]

Yep there is "DPMS pattern", and there is DPMS brand.  No guarantee that the dimensions are the same across the pattern and the brand. 

[survivalshop]

1 hour ago, mrmackc said:

Yep there is "DPMS pattern", and there is DPMS brand.  No guarantee that the dimensions are the same across the pattern and the brand. 

 You can say that again . About sums it up .

[CentralNChunter]

Before I went to email Thunder Guns I wanted to verify my measurements.  I wasn't sure which print I looked at for dimensions (and posted the wrong link when I intended to post link to print in first post) I looked at the few DPMS pattern prints Google pulls up.  On one my slot is 0.010" higher (sketchy looking print and not sure how accurate). Couple other prints my mag catch slot is 0.008"-0.012" lower than print spec.  Called a friend and his PSA G2 mag catch slot is 0.015" higher.  Not sure if 0.015" would cure my issue or not.  Sure wouldn't hurt, but if I were to make a mod to the receiver and make a new mag catch I would likely go 0.040" higher for starters.

survivalshop, I'm not sure a different mag catch would help.  I can't imagine how the Armalite catch would hold the mag up higher any meaningful amount. There is zero play between the upper and lower.  I machined the trigger pocket to just fit the upper.  To break them apart it takes a light tap with my palm to the buffer tube to separate them. Gap between upper/lower: At front 0.004", at rear 0.002".  Not sure If I got the dimensions you requested, but here goes; from top deck of lower to top of cartridge rim is 0.4195".  From deck of upper to bottom of barrel extension is 0.1595"

[98Z5V]

15 hours ago, CentralNChunter said:

98Z5V , if you have DPMS pattern print specs that is different than what I have came up with, I would be glad to accept a copy to compare to my parts. Sounds like I didn't use the brand or retailer you are partial to. From what I found on the web, my parts are in spec for DPMS pattern, but as you stated in another post, 308AR is not standardized & companies can make whatever they want.

Don't take my comments personally, as an insult to you.  It appears you did.

All I was saying was look at the company you bought the parts from - I pointed you in the direction, even provided a thread link with information.  Someone else just asked about this company recently, and I'd never heard of them - so I researched.  I didn't come up with a whole lot of good feedback, either, no matter how you slice it.  Reminds me of reading reviews of Vulcan/Hesse/Blackthorne products.

Now, all I said was that if you have multiple issues going on, there may be no way we can diagnose all that over the web, pictures or not, accurate descriptions of the issue or not, and leave you with a perfectly functioning rifle - and it doesn't look like you're going to get help from the company you bought your parts from.

SO, in a nutshell, don't be butthurt by what I said - you bought the cheap kit.  If it's something simple, we can probably help you - as I stated earlier, looks like what you have planned might work.  If it's a combination of cheap parts from a cheap company that you received for a cheap price...  there may be no help in that situation.

If you search here, we collectively just went through a bunch of tech info on the comparison of DPMS-based 308 bolt carriers vs. Armalite AR-10 based bolt carriers, as well astheir respective bolts.  That info is here.  Measurements, specs, and enough to make your head spin.  There is no "print" or "spec" that you'll be able to solidly refer to in the large frame ARs - because there is no set spec for them. Use the info we came up with as a basis on what should appear normal for your design base of the BCG and bolt.

You've heard of the Machinist's Rules, I'm sure...  The exact same thing goes for firearms parts...

 

 

Edited May 25, 2017 by 98Z5V

[CentralNChunter]

Failure to Feed issue is resolved.

98Z5V, I wasn't butt hurt, but could not let the out of spec assumption pass without responding.  I come from a QA Lab background.  My point was even if you think a part is crap, it is not crap until part dimensions are compared to print spec's. Yes, the receiver set and bcg were purchased because they were on sale / cheap, as Christmas gifts from the wife.  If the only option was a $300+ receiver set and $250+ bcg, well I wouldn't have attempted a AR308 build as I have no real need aside from just wanting to put one together.  From Christmas gift parts, friend giving me a $250 Midway gift card for my birthday, I have very little out of my pocket invested ($300? don't remember what it tallied up to).

I will note (attempting to) dealing with Thunder Guns has not been a pleasant experience.  I emailed them with a video, pic's and CAD drawing of my mag catch slot in relation to the receiver top deck and pivot/take down holes.  They would not respond to email, but requested I call 9am-4pm for further assistance.  I work from 6:30-4.  With 10 minutes of lunch break left I called, 2/3 of that time spent on hold.  As my break ended, the third person to come to the phone, the resident "gunsmith".  I thanked him but informed him my break was over and hung up.  I called at 4:15 but was told by the person that answered, everyone else had already left.  I emailed again and got the same please call response.

I machined part of the mag catch slot higher and made a new mag catch.  My catch even has full engagement with the button, unlike the three threads the DPMS catch had.  I moved the magazine up 0.040"  Shot 30'ish rounds without any failure to feed.  Had failure to eject but will expand on that next.  Mag catch was machined from some mild steel flat stock I had on hand.  The threaded stud was from a grade 8 screw.  The end that went into the catch was turned down to 0.125" and high temp soldered to the catch.  I believe this fix's that issue.  It looks a little like butt now, but once the gun is determined to be reliably functional, I'll likely Cerakote the gun in some camo pattern.

[CentralNChunter]

I think I have one last issue to work out, one that seems to be somewhat common on some DPMS/PSA guns from my limited search.  That would be the good 'ol failure to eject.

As I was testing for feeding issues, I turned out the gas screw a half turn every 5-10 rounds.  That may have made it worse, but I'm not really sure with the limited rounds used.  Ejection pattern is around the 3 o'clock range.  I found the AIM bcg extractor cracked.  I went ahead and ordered a Gen 2 DPMS extractor (supposedly backwards compatible), ejector & spring.  Reviews I read were pretty positive on this part fixing ejecting issues of others.  I emailed AIM, but as this was a Christmas gift, ordered 6 months ago, I don't really expect them to do anything about it, unless there was a known issue of a run of bad extractors in their bcg's.

Looks like I won't have to work this Saturday, so maybe I can get back out to the range with the new parts and see how it goes.  I'm going to run the gas screw in until the bolt doesn't lock back on an empty mag, & start turning the screw out from there.  Question, does the average (if there is such a thing) 308 AR have a 2-4 o'clock ejection pattern similar to AR15's?

video of failure to eject: https://www.dropbox.com/s/gdte6tcjv5u1ag3/Failure to Eject vids and pics.mpg?dl=0

Edited June 1, 2017 by CentralNChunter

[98Z5V]

25 minutes ago, CentralNChunter said:

 I come from a QA Lab background.

From what I understood about Thunder Guns, they certainly DON'T come from a QA Lab background - that was my main point.

In my limited research on them previously, it's not just one thing - it could have been many things.

From your original description of what you found, and what you proposed as the main idea of the fix, it sounded logical to me as explained.  Glad it worked out. 

[bubbas4570]

CentralCNhunter,

Looks are secondary,  function first!  If the part works, that is all that matters, paint/blueing/ceracoat/ECT., is all nothing but coverings for pretties.

No animal is going to give 3 craps about whether your bolt catch looked good, but it will care more about your rifles correct function.  And some POS is much more likely to care about failures, if that happens to be the tool 8n your hand when needed.

[survivalshop]

    If you want some good replacement components for your Bolt , D.Wilson makes very good Parts kits http://www.dwilsonmfg.com/store/c5/AR10_Parts.html . Many here use them & his BCG's .

  I had a very early CMMG Lower Receiver that the first LR308 Pmags would not work & caused the same feeding issue you have/had . This Lower had no feeding issues with any Steel Mag used , several makes were tried & all worked , including Lancer L7'S, but not Magpuls . Found discrepancies in the height of the top Cartridge in the Mag ,off the Lower Receiver top Deck , I have to get my notes out to give exact measurements , but found it doesn't take much for a Bolt over Failure to feed , the Bolt slides over the Cartridge Base & the front of the Bolt Carrier catches it & you have seen the result .

   Tolerance stacking in these 308AR made Receivers is a large issue , I did three things to fix or correct the issue ( well Magpul did one of them ) I bed the action to take up excess play between the Upper & Lower Receivers , including Shimming front Pivot Pin between the Receivers , used an AR 10 Armalite Mag Catch , which has a larger locking Pad area & as said , Magpul came out with a Gen. 3 LR PMag , they lowered the locking point on the mags , mag Catch recess & its stop , raising the bottom of the highest Cartridge in the Mag for a better feeding level & not interfering with BCG travel .

    Rifle functioned flawlessly after that , with all mags , even the original Pmags .

 Your issue is somewhat the same , but more extreme , it seems . I don't blame CMMG or Magpul for the issue with my rifle , because when CMMG made /designed the Lower , only Steel Mags were available , Magpul didn't come out with the LR version if the PMag for many years after I built the rifle with a CMMG Lower & at the time CMMG didn't build complete rifles , only Receivers .

Edited June 1, 2017 by survivalshop

[CentralNChunter]

30 rounds of success.  20 rounds shot relatively slow fire in five shot groups and 10 rounds shot rapid fire (as fast as I could).  I replaced the AIM BCG extractor and springs with the DPMS upgrade assembly LR-308 GII.  The AIM ejector had what I felt like sharp edges.  I slightly beveled and polished the ejector edges just to be sure it wasn't binding in its bore.  I ran the gas block adjustment screw in and started backing it out a half turn at a time until the bolt locked back correctly on an empty mag.  I then turned it out a quarter turn, hoping this extra gas would keep it functioning after being shot awhile and running "dirty".  I'm thinking of turning it back in a quarter turn though as I'm not sure that quarter turn is needed.  What do you all think?  The brass is ejecting at 3 o'clock, landing (4'-6'?) away, in roughly a 2' radius. 

10 shot rapid fire vid: https://www.dropbox.com/s/z084k8b3gsweifs/308AR 10rd Rapid Fire.mpg?dl=0

While shooting the five shot groups, I got one cool screen shot of a case ejecting.  Seems pretty good to me, but being 308 AR inexperienced, does this ejection/deflector contact look correct for the 308 platform?

 

[Untilvalhalla75]

First off, I have lots of experience with 308’s in the AR platform. From using an issued KAC in country, to building a KAC clone, and building dpms pattern AR’s. 

 

Ive built a 20” 308 using thunder tactical’s 80% lower and complete upper. All I’ve done different was an adjustable gas block, an armalite rifle length gas tube(longer than dpms) and buffer/spring changes. My TT 308 is just as reliable as any of my other 308’s.  

 

Its definitely a great base gun. It keeps surprising me on the accuracy. I’ve shot clay pidgeons at 800m+ and nail them in one, at most two shots using a 4.5-18x scope. 

So just because it’s cheap, doesn’t mean it’s garbage. Change your BCG, get an adjustable gas block, make sure your gas tube is sitting in the key far enough. Armalite tube is slightly longer to fix this. 

Buy an armalite magcatch (Type A) 

iron out the details and you’ll have a greatly priced 308 that’s a tack driver. 

 

Thunder tactical has always responded to my emails and phone calls fast. Maybe you called on a bad day. 

 

Also, pour a bunch of CLP on the BCG and use lithium grease in the buffer tube. Keep up with the CLP until you’ve hit 500 rounds. It works wonders 

[Sisco]

That is the Mother of all flash hiders. Interested in the story behind that.

[COBrien]

29 minutes ago, Sisco said:

That is the Mother of all flash hiders. Interested in the story behind that.

I think it's intended to be used with a, ahem, "blast deflector" shroud placed over it.

For flash reduction purposes, and definitely not anything else.

[jtallen83]

6 minutes ago, COBrien said:

For flash reduction purposes, and definitely not anything else.

+1^

 

8 minutes ago, COBrien said:

 

36 minutes ago, Sisco said:

Interested in the story behind that.

We don't want much discussion on that. Guy selling something very similar on ebay got a visit from ATF.....

@Untilvalhalla75

[Sisco]

Gotcha

[shepp]

5 hours ago, Untilvalhalla75 said:

First off, I have lots of experience with 308’s in the AR platform. From using an issued KAC in country, to building a KAC clone, and building dpms pattern AR’s. 

 

Ive built a 20” 308 using thunder tactical’s 80% lower and complete upper. All I’ve done different was an adjustable gas block, an armalite rifle length gas tube(longer than dpms) and buffer/spring changes. My TT 308 is just as reliable as any of my other 308’s.  

 

Its definitely a great base gun. It keeps surprising me on the accuracy. I’ve shot clay pidgeons at 800m+ and nail them in one, at most two shots using a 4.5-18x scope. 

So just because it’s cheap, doesn’t mean it’s garbage. Change your BCG, get an adjustable gas block, make sure your gas tube is sitting in the key far enough. Armalite tube is slightly longer to fix this. 

Buy an armalite magcatch (Type A) 

iron out the details and you’ll have a greatly priced 308 that’s a tack driver. 

 

Thunder tactical has always responded to my emails and phone calls fast. Maybe you called on a bad day. 

 

Also, pour a bunch of CLP on the BCG and use lithium grease in the buffer tube. Keep up with the CLP until you’ve hit 500 rounds. It works wonders 

Welcome to the forum not sure why you nechro’d this thread but feel free to tell us about yourself In the intro section