LR-308 build, with fully closing bolt issues

[waterman7474]

I am working on a new lr-308 build and have had a few issues and am now dealing with this issue.  I thought I would try here as solutions seem to have dried up on the other site and maybe I will get some fresh perspective here.  I will link to the other thread (if that is ok) to save me retyping this as I think the history has bearing on the issue. 

 

first issue

http://www.ar15.com/forums/t_3_121/603919_new_lr_308_build_with_mild_extraction_issues.html&page=1

 

If you followed that to the end of page two, the problem in a nut shell is this: 

 

The ejection issue is fixed, drops them every time in the same place,.....but now the bolt doesn't go all the way home to lock after the first shot. It seems to get 90-95% there and jams. I have to mortor it a little bit to get the handle back. And if I pull it all the way back and let it go, it slams home fine.

It actually double fired on me once, full auto style, bam bam. Luckily I was just out in the desert cause it startled me a little and would have certainly raised and eyebrow if I had been at a range.

I was then asked to look into the spring and buffer and came up with this.

 

so I was given two different springs and two different buffers.  This is a magpul moe rifle stock, with the A2 buffer tube.

buffer A - 5.25 in, silver and has a ring 1/3 way from the end (like a duplex nail)
buffer B - 5.0 in, black smooth like a longer ar15 buffer
neither are marked

Spring A - 12 in, 38 coils and thicker (than the other one and my 15 buffer)
spring B - 17 in, 41 coils and thinner

I had spring A and buffer A.

I am thinking that buffer A is correct but i should be using spring B

 

 

 

The (very helpful so far) engineer at JP seems to think that spring and buffer A are dpms 308 stock kit and B are KAC kit and that I shouldn't mix them. 

 

He seems to think that maybe there might be an issue with one of the locking lugs on the barrel extension. 

 

I am outside my sandbox now.  Any thoughts?

 

Thanks in advance,

 

 

[EasyEJL]

buffer A sounds like a normal rifle buffer, buffer B could be a carbine buffer or rifle, hard to say. weights might tell a story too. 12" sounds short for a rifle spring, but 17" sounds a bit long to me. I've only got carbine lengths here to measure. But i'm just going off memory

[washguy]

Hi Waterman I just measured a new ar308 rifle buffer 5.25 inches new 308 rifle spring 12..75 inches
so you could have a mixup in the spring/buffer....always function check with 1 round in the mag ....fire then see if the bcg locks back.... that will tell us some things....prolly your spring,but it could be the gas tube not lining up with the carrier as it goes into battery.....take the upper off the lower....point the muzzle down and drop the bcg into the upper...it should go into battery or very close into battery..look for the gas tube slowing things down if its not lined up spot on...also take the bcg out and put in the charging handle to see if it slides smoothly onto the gas tube.....always start with one single round to see whats going on...gotta lock back...... also you can blow air down from the muzzle with the chamber blocked  and put your finger on the gas tube inside the upper to check for the gas block being lined up .....Wash

Edited April 16, 2013 by washguy

[waterman7474]

Thanks.  I will try most of these tonight in the garage (except the firing and lock back....)

 

Let me know what yall find on the springs.

 

I was going to swap them out but Dave from JP said this

 

That actually sounds like it was correct. Buffer A sounds like a standard DPMS 308 buffer and Spring A sounds like a DPMS 308 spring as well.  The B parts sound like Knights Armament parts. They use a longer spring and a simple plastic buffer that looks like a long carbine buffer as you describe. The duplex style as you put it is more typical for a rifle buffer from everyone else.  I have never tried a KAC  buffer and spring in any other rifle but they are actually pretty similar in final spring rate, but don’t mix the KAC spring with the DPMS buffer or vice versa.

 

I don't guess it could hurt to swap out the spring and try the longer one.  I am pretty sure I am using the correct buffer.

 

And I have my suspicions on lining up the gas tube.  As you can see from the first page of the arf post, it was off once before but I feel like i got it on correctly.  It is so hard to tell with a clamp on block.

[waterman7474]

Hi Waterman I just measured a new ar308 rifle buffer 5.25 inches new 308 rifle spring 12..75 inches

so you could have a mixup in the spring/buffer....always function check with 1 round in the mag ....fire then see if the bcg locks back.... that will tell us some things....prolly your spring,but it could be the gas tube not lining up with the carrier as it goes into battery.....take the upper off the lower....point the muzzle down and drop the bcg into the upper...it should go into battery or very close into battery..dropped in just fine

 

look for the gas tube slowing things down if its not lined up spot on...looks good

 

also take the bcg out and put in the charging handle to see if it slides smoothly onto the gas tube.....smooth, no hanging

 

always start with one single round to see whats going on...gotta lock back......also you can blow air down from the muzzle with the chamber blocked  and put your finger on the gas tube inside the upper to check for the gas block being lined up .....seems ok.  not sure it if it is fully lined up though  Wash

 

i will try the bolt locking back this weekend.

 

I put the longer spring in.

 

i am begining to think this might have been the issue and i got them mixed up.

[edgecrusher]

 

 

This is my link to my experience with our site sponsor's buffers and he uses Armalite springs, and what a difference they make. I'm not telling you to go out and spend the money, I put measurements and weights up for all to compare to. 

 

PURE QUALITY!

[texas30cal]

At first mine had a hard time closing the last 3/8"-1/2" when chambering a round, it closed fine without a round in it. It turned out to be a rough chamber and I believe a little on the tight side because it got better with polishing the chamber but completely went away when I switched to small base dies.

[seasprite]

Are these reloads or factory ammo that the bolt won't close on? If its reloads you might not be setting the shoulder back far enough. I had a similar problem that I could not unload a live round without mortaring the rifle because I was jamming the shoulder. Do you have a case gauge if not you can try smoking the shoulder to see if your jamming it. Check this link the case on the left is just a smoked case, the middle is when the shoulder was jamming and the right is where my shoulder is set back enough to properly cycle the bolt without mortaring. 

 

 

http://forum.308ar.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=5157

 

    

[waterman7474]

Are these reloads or factory ammo that the bolt won't close on? If its reloads you might not be setting the shoulder back far enough. I had a similar problem that I could not unload a live round without mortaring the rifle because I was jamming the shoulder. Do you have a case gauge if not you can try smoking the shoulder to see if your jamming it. Check this link the case on the left is just a smoked case, the middle is when the shoulder was jamming and the right is where my shoulder is set back enough to properly cycle the bolt without mortaring. 

 

 

http://forum.308ar.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=5157

These is factory ammo.

 

So I just went out.  Switched to the long spring and standard buffer.

 

Not great.

 

First shot, two rounds, 95% closed bolt.

 

Then tried one round to see if bolt locked back.  It did.

 

Ran two more through, 95% closed on second, then didn't lock bolt back. 

 

Ran two more, went full auto.

 

Ran three, full auto (fun....but concerning)

 

Ran two, bad ejection

 

Then two more bad ejections.

 

I am lost....

[imschur]

Sorry I dont have time to read the history ATM. Looks pretty dry...run this thing really wet with Mobil 1. Armalite AR-10 buffer spring as someone else mentioned. Heavy buffer site spells out springs as well as buffer weights and possibly imensions

[washguy]

Hi Waterman    starting to sound like a rough tight chamber....time for some flitz polishing in the chamber i use a shotgun cotton type swab on an electric drill with flitz. so you got it to lock back once? hmmmm......the auto fire concerns me...you sure you got your disconnector spring right side up? and what kind of trigger group? any marks on bottom of the carrier or on top of hammer? disconnector spring has a fat end and a smaller end...fat end goes down.  Oh btw have you got the extension installed in your a2 stock?  Wash

Edited April 21, 2013 by washguy

[waterman7474]

Hi Waterman    starting to sound like a rough tight chamber....time for some flitz polishing in the chamber i use a shotgun cotton type swab on an electric drill with flitz. so you got it to lock back once? hmmmm......the auto fire concerns me...you sure you got your disconnector spring right side up? and what kind of trigger group? any marks on bottom of the carrier or on top of hammer? disconnector spring has a fat end and a smaller end...fat end goes down.  Oh btw have you got the extension installed in your a2 stock?  Wash

Thanks,

Flitz was the first thing I have done, recommended from another site.  Twice actually. 

 

one of the ARF guys suggested the springs too.  I will take it apart and look there.  maybe i reassembled wrong.  i did a little light dremmel (with a wire wheel) on the sear, to try and take some of the grit out.  could that be the auto fire issue?

 

took the extension out, using the new magpul fixed stock.

[survivalshop]

It doesn't take much to screw up the sear engagement surfaces  . The disconnect should stop the hammer from dropping with out releasing & pulling the trigger again.

[washguy]

Thanks,

Flitz was the first thing I have done, recommended from another site.  Twice actually. 

 

one of the ARF guys suggested the springs too.  I will take it apart and look there.  maybe i reassembled wrong.  i did a little light dremmel (with a wire wheel) on the sear, to try and take some of the grit out.  could that be the auto fire issue?

 

took the extension out, using the new magpul fixed stock.

 

Hi Waterman      yeppers on the sear causing auto fire prolly so.....make sure the disconnector spring is installed correctly....okay so you got it to lock back onc...thats a good thing,but then it stopped locking back right?  Im not familar witha magpul fixed stock...so you put the new magpul stock in before you took it out to the range this time?   if so you are creating problems without solving issues....one thing at a time...you didnt tell us you messed with the trigger group....lol    so does the shell chamber nice and sweet on the first time you charge it? if so the chamber with you polishing twice should be okay.... if it were me i would put the good ol trusty a2  withe extension back in to get the kinks out ....when you are having cycing issues one thing at a time is my motto    Wash

[blue109]

Any chance you can find a local to swap BCGs with? I chased bugs for months that turned out to be a out of spec bolt. The cam pin hole was slightly off. The fine folks (sarcasm) at JSE surplus took the bolt back after my initial problems and said they tested it in two other rifles before sending it back to me. Obviously they were full of it because as soon as I dropped the new bolt in everything was butter.

[waterman7474]

 

 

I will try this with the old stock, although....the extension goes on the outside of the tube and shouldn't effect the spring or any other function at all right??

 

I am thinking I might have to just start with a new trigger group now, maybe I messed it up.

[waterman7474]

Any chance you can find a local to swap BCGs with? I chased bugs for months that turned out to be a out of spec bolt. The cam pin hole was slightly off. The fine folks (sarcasm) at JSE surplus took the bolt back after my initial problems and said they tested it in two other rifles before sending it back to me. Obviously they were full of it because as soon as I dropped the new bolt in everything was butter

Most of this problem started with the bolt issue from JP.  There were issues with the ejector/extractor.  It seems to be ejecting better but not perfect.

 

The carrier is Fulton Armory.  I guess it could be something there.

[waterman7474]

Decided to take it to a gunsmith. He is scratching his head. I definitely had the wrong spring (he had an in the package dpms 308 spring and it was different than the two i had). The thought it might have been from shooting too light of a load, ran some russian surplus 180 grain stuff and didn't eject at all.

He's gonna do a complete teardown and re-build.

Thinks the auto-fire might be from me "cleaning up" the trigger. I knew better but did it anyway for some stupid reason.

[waterman7474]

So it looks like the gas block was not correctly lined up and the disconnector spring in the trigger had gone walkabout and causing the auto-fire issues.

Between that and the new spring, runs like a top now.

Thanks for all the help guys.

Hopefully this will help someone else out down the road.

[washguy]

thats what we all here for....glad we could help...have fun with the beast! :auto:   Wash