My MATEN build

[mordak6actual]

So I built a MATEN.  I will just summarize from the other posts and condense here to minimize the hunting for the various topics.

Long story short, here is what it was doing (in order of the problems from start to finish):

 

- recoil caused the bullet button to self-disassemble (this was an easy fix)

- On about the fifth or sixth round, the entire gun seized and refused to go into battery.  On takedown/evaluation, the extractor pin had walked and then deformed from the force of the bolt unlocking and rotating into the carrier (diagnosed as bad extractor springs, not providing enough tension to hold the extractor pin in place and keep it from walking)

- not going into battery from an open chamber with bolt locked to rear, magazine in well.  Hit bolt release, it would not lock up without having to push on the bolt to get it to go into battery

- Not going into battery after the first or subsequent shots (same problem, have to push on the bolt to get it to lock up)

 

Here's a picture of the offender:

Here's the parts list:
MATEN upper/lower matched receiver set

RA-SEL-308-16 Rainier Arms Select .308 16" 416R Black Stainless Barrel - DPMS Pattern

RF-M-GasTube Radical Firearms Stainless Steel Gas Tube - Mid Length

308-BCG-NiB Radical Firearms Complete Nickel Boron Bolt Carrier Group for .308 with WMD Coating

05-199 ALG Defense Combat Trigger - ACT

RF308CARB Radical Firearms .308 Carbine Buffer - 3.8oz

DP308-CS-10A DPMS .308 Carbine Buffer Spring - 11.5 Inch

LR-01 Black Rain Ordnance Buffer Retaining Pin

LR-02 Black Rain Ordnance Buffer Retainer Spring

SP0011510031 Seekins Precision Low Profile Adjustable Gas Block .750

Magpul UBR 

14" Parallax Tactical fore-end

Griffin Armament 7.62 Flashcomp

So, here are the things I bought to troubleshoot my issues:
- different magazines (Magpul PMAGs to Lancer L7)

- another NiB BCG (Radical Firearms)
- a Heavybuffers.com buffer and spring

So I wanted to take the rifle to Randall from ar15barrels.com to see if he could take a look at the gun but he had a few suggestions to try first.
- run it without the buffer pin/spring
- try different ammunition
- load a single round into the magazine, load from locked back bolt.  Repeat 5x. Report back.

Nothing he suggested worked.

What ultimately fixed it was changing out the carriers (last resort).  The old and new BCGs were both Radical Firearms.  The old one had a narrower channel where the hammer would fit.  The new one had a wider channel.  On a hunch I swapped them.  Ran the gun with the DPMS carbine buffer spring and original buffer.  Gun now runs fine (at least I can shoot the thing like a semi-auto).

I'm not sure what was going on at this point.  I was thinking the carrier was rubbing against something it shouldn't have been rubbing against, but that doesn't make sense if the hammer is locked downwards, ready to fire.  I cranked up the gas port as open as it would go, but my problems started even before firing with the bolt not locking up.  With the new carrier, the bolt locks up every time, no problems.  I have a set of .308 headspace gauges coming in so I will verify there are no problems, but I figured that if the thing hasn't blown up in my hands after 50+ rounds or so, I should be relatively ok.

I also noticed, ironically that I have less problem with 7.62x51 versus .308 (from Freedom Munitions).  The surplus 7.62 wasn't causing extraction issues while the .308 was.  By now I am running the Heavy Buffers spring and buffer, gas port cracked all the way open, and that seems to be the way to keep the gun working.  Just hopefully I am not missing something or overlooking something.

All in all this has been a learning experience and a little bit frustrating.  Coming from the AR-15 world, things just worked and they were easier to troubleshoot (never had to get into buffer springs, weights, etc.).  I guess having a TDP out there as a baseline for manufacturers to ensure compatibility is a good thing and it's unfortunate this never made it to the .308 AR world (or at least have OEMs make their own with regards to receiver dimensions and internal parts, but that's just wishful thinking).

[mrraley]

OK... I'm unclear on exactly what buffer and buffer spring set up you are currently using.

 

Could you elaborate on that and possibly post pictures and sizes please?

 

 

 

But form what I can tell just from the picture alone and what you have described is... your problem is in the buttstock / receiver extension tube.

 

The UBR is specifically designed for the AR-15 style of rifle. There are modifications to allow the short tube to be used on the larger caliber though.

 

 

Here is something in a way for you to check.

 

**Make sure your buffer and buffer spring are in the rifle.**

 

Pull the charging handle to the rear, locking the bolt back with the bolt catch.

 

Look inside the rifle either through the ejection port or the mag well and see where the bolt stop is holding the bolt at.

 

Is it on the carrier under the bolt? OR is it in front of the bolt face?

 

If it is on the carrier, the receiver extension tube is short and you need a cut spring and short buffer.

 

If it is on the bolt face as it should be, you have the proper spring and buffer for the short receiver extension tube.  BUT... your buffer might be a little light.

[survivalshop]

  We have been seeing a lot of NIB bolt /Carrier problems with too thick of NIB coatings . Sometimes the coatings are bunched up in places . Some Manufactures seem to work with the NIB coatings , some don't , I will not use a NIB coated Bolt any more , I like the Nitrated ones , DWilson makes a very good product in both NIB & Nitrated or you can mix them up .

http://www.dwilsonmfg.com/store/p18/AR10_Bolt_carrier_Group.html

 

  With the Buffer assembly ,  a 308 Carbine specific DPMS  , spring & Buffer , it should work . The Heavy Buffer's Buffer & spring as long as its for a DPMS 308 Carbine type Receiver Extension , should work also .

  The UBR comes with its own Receiver Extension , an AR 15 Carbine type . 

[mordak6actual]

So I'll put up a few more photos to show what I'm talking about:

 

At left, old carrier, right, new carrier.  Bolt was swapped (old bolt w/new carrier, and vice versa).  I couldn't get the gun working (or into battery without pushing on the bolt) with the carrier on the left.  These are both from Radical FIrearms but the left one has a much narrower channel for the hammer.

To answer the question, here are the two springs.  One was the original and the other (on the right) is the currently used Heavybuffers.com heavy buffer and spring.

Almost a difference of 2 oz. between the two buffers (3.8 vs. 5.7).  Springs appeared to be equal length (and were advertised as carbine length .308)

 

The tops of the bolt carriers.  Not sure if that is relevant or not.

 

And finally, another picture of the rifle fully kitted out:

[mordak6actual]

Oh and bolt stop is on the bolt face not the carrier. But that's true for both of them.

[blue109]

Gorgeous rifle. Well done. I've never see such a small channel on a BCG. Could certainly be an issue there

[98Z5V]

Slash specs out the Armalite EA1095 spring with his heavy buffer, for use the in the UBR on a .308AR.  If you ordered the buffer and spring from him, that's the spring you received.  It's a solid combination, and won't be the source of your issues, in the least. 

[mrraley]

any update on progress?

[shazam]

i am curious as well.