First build...possibly complex issue

[kazuaki]

** Sorry  for the long post, but I'm trying to be as detailed as possible on what seems to be a complex issue. **

 

Hi all, I just completed my first LR308 build.  I have previous experience with several AR-15 builds, including a few 80% lowers.  For this 308 build, I used a Juggernaut Tactical upper and 80% lower.  After completing the lower and assembling the rifle, all seemed to be good.  Today at the range, after firing 30-40 rounds, I had a couple of FTF due to light strikes. I stopped and decided to pull the BDG and look things over.  When I tried to remove the firing pin, it was pretty well stuck in the bolt.  I had to pull it out with a set of needle nose pliers.  As soon as it came out, about a dozen small round metal bits came pouring out of the bolt tail. After consulting with another shooter, we went and looked at my spent brass.  Many of them had a hole clear through the primer. I guess the piece punched out of the primer was flying back into the bolt through the firing pin hole.  It eventually bound up the firing pin enough to cause the FTF's.

 

So, I called it a day and headed home to troubleshoot.  I measured the firing pin protrusion and it is about 0.055", which I believe is OK.  Can anyone confirm that? I found a post on another forum, where a guy had issues with light strikes due to the hammer hitting the bolt catch, thus not putting full force into the firing pin.  I checked mine and, sure enough, with the hammer dropped, the bolt catch is binding.  The hammer rests on the bolt catch, not the firing pin.  Obviously it strike the firing pin hard enough to send it flying forward and hitting the primer.  Most of the time it ignites.  My fix for this was simple, I machined a very small amount (0.025") off the back of the bolt catch.  Basically, I removed the small lip on the rear of it.  I can now drop the hammer and still move the bolt catch freely.  Success, right?

 

What still bothers me is the pierced primers.  Assuming the pin protrusion mentioned above is OK, what could cause that.  Could the fact that the firing pin is not being held firmly against the primer allow the primer to blow out? When my firing pin struck the primer, it would immediately fly back t the face of the hammer, which was at least 02" away. Could that cause the center of the primer to blow out?  I know the easy answer is to go back to the range, but with life getting in the way, that's not so easy :)

 

So, what do the expert think?

 

PS, can somebody take some accurate measurements of an LR308 firing pin? I'd love to know the overall length and the length from the tail of the bolt rearward.

 

Thanks!

[MikedaddyH]

Need a little more detail on some of the parts :

BCG brand ?

FCG ? Trigger and hammer springs ??

Possible fixes: extraction spring/O-ring needs wear/break in.

Firing pin too long ... 1mm or 2mm max.

Chamber tight not not broken in yet, also sounds like it was run dry...not wet enough(oil running down you arm and dripping on the floor wet) Remember this is not an Ar15 !

Give us these extra details then we should be able to eliminate some of the issues.

[shepp]

I'm by far no expert but maybe the brand of ammo you were using?

[kazuaki]

Sorry, for the lack of details.

 

AIM Surplus BCG

Wilson Combat TTU 2-stage drop-in trigger group

Pretty sure it was run wet enough.

 

I'm curious, how could the extracor spring/o-ring being stiff cause this? Just to be clear, there were no failures to extract or eject. I'm 100% positive that the hammer face was sitting on the bolt catch. I'm pretty sure is should be resting on the firing pin only, correct? I can confirm that when I dry fire it now, the bolt catch does not bind and can be moved freely. So, I think I'll be getting full power to the firing pin now.  The big question that remains for me is about the pierced primers. Can somebody confirm the .055" firing pin protraction is acceptable? Also, can a free-floating firing pin (not being held against the primer by the hammer) allow the primer to blow a circle out the back into the bolt?

 

Thanks again for the help.

[kazuaki]

Sorry, forgot about the ammo too.  I used 3 types of ammo: Perfecta 7.62 147gr from Walmart, Federal Gold Medal Match 7.62 175gr, and Eagle Eye 308 175gr.  The Perfecta primers were intact, I suspect because they are harder maybe. The Federal had 1 or 2 primers pierced and the Eagle Eye had about 75% pierced.  That being said, the Eagle Eye was also the last ones I shot.

[kazuaki]

OK, more info I just discovered. I'm fairly certain that Juggernaut drilled the buffer retainer hole too far rearward.  If you look at the first picture, you can see the buffer sits perfectly flush with the lower. Shouldn't it stick out a little, so that the back of the BCG pushes on the buffer and takes tension off of the buffer retainer when closing the upper? In addition, you can see the damage to the buffer from slamming into the retainer while firing.

 

 

[EasyEJL]

that part should only affect perceived recoil and not affect the forward motion of the bcg, although it is a problem. realistically, the "plus" is that if you every so often rotate the buffer it will end up pounding itself out so long as it doesn't break the retainer in the process :D other thing you can do is machine the ring around it to the depth of what is already pounded out and it should be fine

[survivalshop]

  I measured two Bolts the other day for Firing Pin protrusion a used DPMS & a New DWilson Bolt , the DPMS was 0.052" & the DWilson was 0.058" , so your in the ball park.

 New DPMS firing Pin is 3.941"

 Tail of the Bolt forward, measurement  ? Explain. <dontknow>

 

  You have an 80% lower , I have no experience with them & really don't want any , but you having to machine material off the Bolt Catch on the side that catches the Bolt may cause another problem , like catching the Bolt. <dontknow>

 

  Just looked at your photo of the Buffer , we have seen damage like that before , is the BCG pushing the Buffer back into the Receiver Extension a little when closing the upper onto the Lower ?  In operation the Buffer should never hit the the retainer pin !

Edited August 3, 2015 by survivalshop

[kazuaki]

survivalshop, thanks for confirming the protrusion measurement.  I know that having to machine the bolt catch is not ideal, but it was only .025" off the back face of it.  It's still just as tall as it was before, so I don't see any other issues.  I wish I didn't have to do it though.  Now that I've discovered the issue with the buffer retainer (that comes machined already, not done by me) I have lost some confidence in the rest of the lower's quality control.

[kazuaki]

survivalshop, the bcg does not touch the buffer at all when closing the upper.  The buffer face is perfectly flush with the lower.  I think it should be protruding a bit when resting on the retainer.  I'm pretty sure they put the retainer hole in the wrong place (Juggernaut's doing, not mine).  That being said, I'm not certain it is related to my original issue.

 

 

[survivalshop]

  More likely the Upper Receiver , the BCG is going to far in , we have seen it before , you can fix it , there is a weight system you can add to the Bolt Carrier , don't remember the name ,but someone here will . Easy fix & not expensive if my memory serves me . <thumbsup>

[kazuaki]

When the BCG is in battery, the back of the BCG is flush with the rear of the upper receiver.  I believe that is how it should be. Can somebody break open one of their LR308's and tell me if the face of the buffer protrudes from the lower when resting against the buffer retainer?

 

Here's a picture of my BCG in the upper:

 

 

[kazuaki]

Here's a picture of some of the primers.  Left to right, Eagle Eye > FGMM > Perfecta.  Notice the Eagle Eye has the hole in it.  Also, some of the brass has a pretty noticeable scratch/smear mark from the ejector.

 

 

[jtallen83]

  More likely the Upper Receiver , the BCG is going to far in , we have seen it before , you can fix it , there is a weight system you can add to the Bolt Carrier , don't remember the name ,but someone here will . Easy fix & not expensive if my memory serves me . <thumbsup>

http://www.davidtubb.com/carrierweight-ar15

 

Fits both ar-15's and 308AR's

Edited August 4, 2015 by jtallen83

[DNP]

Mine protrudes about a 1/16 at the top.

And here they make contact on closing.

[shepp]

Mine protrudes about a 1/16 at the top. image.jpg

And here they make contact on closing. image.jpg

Mine too Edited August 4, 2015 by shepp

[DNP]

You're still talking about your 308, yeah?

[DNP]

Dumb question. Can you post a pic of your retainer? Looking into the tube holding the buffer. How does it sit against it?

[kazuaki]

Is this what you mean?

[DNP]

Yeah. Had to see it. It's like callin tech support and they ask if it's plugged in. I said it was stupid, but had to see it actually meeting up with the right section of the pin. We have exceeded my technical capabilities. I will watch closely as this goes on though. I remember the thread with the beat up buffer like that one -can't remember what the outcome was.

[kazuaki]

I've looked at pictures of other 308 lower including those posted above and verified that the buffer should protrude a bit. So, the buffer retainer hole in my lower is out of spec. I sent Juggernaut pictures, but I can see the ones on their webpage even look like that. Funny thing is the buffer issue isn't even the issue that led me to start this thread. It's the pierced primer issue that is a bigger concern to me. I'll have to get back to the range and see if my bolt catch fix will resolve that.

[survivalshop]

survivalshop, the bcg does not touch the buffer at all when closing the upper.  The buffer face is perfectly flush with the lower.  I think it should be protruding a bit when resting on the retainer.  I'm pretty sure they put the retainer hole in the wrong place (Juggernaut's doing, not mine).  That being said, I'm not certain it is related to my original issue.

 The primer piecing is probably the ammo , if its the only Brand doing it .You keep saying Eagle Eye , is it American Eagle ?

  Hard to tell with the 80% Lowers , There are no MilSpecs on a 308AR like an AR15/16/M4 , Manufacturers make their own up sometimes & can cause all kinds of problems . We have seen a lot of it here with 100% Receivers.

 

 

 Your Buffer hitting the Retainer is going to break it eventually . Does your BCG when locked in the Barrel extension , push the Buffer back into the Lower Receiver Extension when closing the Upper onto the Lower Receiver ? If it doesn't its not to spec's , As said, the Buffer should not touch the Retaining Pin when in operation , with the BCG in locked breach position , the BCG can not go any more forward , so if it can't go forward any more & when closing the Upper onto the Lower , the BCG pushes the Buffer a little off the Buffer Retainer , to keep it from hitting it when the action is cycling . The only time the Buffer should touch that Retaining Pin is when you disassemble or Shotgun the Receivers , its just to retain the Buffer upon disassembly .

 

 Has this rifle had the Head Space Checked ?

[kazuaki]

Survivalshop,

Eagle Eye Ammo:

http://www.eagleeyeammo.com/308-win-175gr-hpbt/

Regarding the buffer, there is absolutely zero contact between the BCG and buffer when closing the rifle. Clearly, that is an issue. It seems we've narrowed that issue down to the lower not being correct. The buffer retainer hole is not to spec. I'm weighing my options on resolving that issue still.

With regards to the pierced primers, I had one round of Federal Gold Medal Match that was pierced as well. Not sure what's up with that. Until yesterday, when I started searching for explanations to all this, I did not realize that a semi auto needed a slightly milder load than a bolt gun. I've read a few things stating that some Ammo might just be too hot a load for the semi auto. I don't exactly understand why or the details of that. I know JP states that their High Pressure bolt was created to address issues with hot loads in these guns.

BTW, yes the headspace was checked with both a GO and NO-GO gauge before the trip to the range.

[survivalshop]

Never heard of that brand of ammo , but I don't buy much ammo , I've been rolling my own for about forty years & pierced or blown out primers are usually the result of over pressure , be it the over loaded ammo or a Bad Chamber . Your firing pin protrusion is correct , so that eliminates that , so your down to Chamber or over loaded ammo . The 308AR's can shoot any Commercial or MilSpec ammo , I have tested a lot of different brands & configurations.

  Your Primers , except for the ones with the holes in them look OK , the ones with holes would not show over pressure , because the primer blew out before it could be flattened from over pressure .

 

  You say you checked Head Space with "No Go' & Go " Gages , check it with a "Field Gage also , just to be sure . Also make sure they are good gages, I have seen , even on this sight , that Chambers passed because of Bad gages , remove the Ejector to test , unless you have a newer set that has a depression in the Gage for the Ejector to fit in . 

 

  Be it the Lower or Upper Receiver out of spec , you can still fix the Buffer pounding with that weight set , easy fix & inexpensive.

This is a new 308AR build & the BCG just slightly pushes the Buffer away from the Retaining Pin.

[kazuaki]

Yes, I actually have new Forster gauges (GO, NOGO, and FIELD) and I checked all three.  The ejector was removed first.