LR308 cycling troubles

[Bill Eckberg]

Good day

i currently have a LR308 DPMS platform with a 20" large barrel and the following, flash suppressor,  DPMS BCG, adjustable gas block, A2rifle stock. 

The BCG does not cycle back

in the rifle stock I have the following

buffer tube is 9.7" long

buffer is 5.2" and 4.8oz

the spring is 12.4" or 34 coils

the last thing changed was the flash suppressor 

can anyone see anything I'm not?

amy help will be appreciated 

[Steve crawford]

I could give you a lot of guesses, but someone that knows a lot more will be along in a minute.   Is this anew build?  Has the rifle ever worked correctly. Pictures of the internals of the upper would help.  That is just a few things that will be asked.  there are guys here that can and will get it going for you.   LMHO   😉😉😉

          Steve

[DNP]

Was it cycling before the flash suppressor change?  Check that the gas tube is installed properly and hasn’t come free. I watched a working gun stop working when a gas tube roll pin broke and released the tube. Check that you haven’t changed something on the adjustable block. Do you shoot suppressed?  

[edgecrusher]

Spring is an AR15 spring and is wrong and your buffer is too light. I’m also inclined to know if this has shot before or is a new build. Receivers? Where does the gas tube fall in the cam pin cut out? This first please

[Bill Eckberg]

Ok the gun is new as of last year. It's an 80% build. It has never cycled properly. I took the suppressor off. I have not shot it yet. My thought as someone mentioned the spring might be to long. That said I'm not sure the buffers weight plays in with not cycling

[Armed Eye Doc]

What exactly are you referring to when you say it is not cycling?  Will the charging handle not come back at all?  Only part of the way?  Comes back but won't lock back?  Won't eject a cycled round?  Won't pick up and feed a round from the mag?

Have you not shot it at all, or just not since changing the muzzle device?

[DustBuster]

Hi Bill, I hope you can get your gun working.  The simplicity of your explanations made me think back to this little cartoon an iron worker friend posted on Facebook once.

Please give more detail for these experts here to help your build.

Take Care

 

[jtallen83]

2 hours ago, Bill Eckberg said:

That said I'm not sure the buffers weight plays in with not cycling

I have to recommend a deep dive in our archives, lots and lots of eye opening reading for you on just the topic of buffer weight alone. Read up, you need to get the basics down before expecting a from scratch build to function.

[DustBuster]

Bill, I see that you posted about your build already, describing some of the issues you dealt with.  You had a bolt catch that was hitting the upper receiver stopping its upward movement.  You solved that by grinding material off the upper.  I’ve had issues before having a bolt catch that went up too high, prematurely stopping the bolt before it could clear the back of the magazine.  I solved that two different ways by modifying the different brand of magazines. I only had that problem with empty magazine bolt stop, not with General cycling.  Hard to know what is fouling you up

[DNP]

1 hour ago, DustBuster said:

Hi Bill, I hope you can get your gun working.  The simplicity of your explanations made me think back to this little cartoon an iron worker friend posted on Facebook once.

Please give more detail for these experts here to help your build.

Take Care

 

Oh crap. Sorry for the unrelated post, but this was beautiful. Thank you for that. I’m a land surveyor and I’ve done a lot of construction layout, and a fair handful of steel erected projects....this is so damn funny because I’ve heard this on half of the sites. “It was. We cut it.”  ...still has me laughing. Everything is wrong, nothing is their fault and nobody has a damn set of plans. 

[98Z5V]

@Bill Eckberg, the other statements about the buffer being too light are correct.  That's a rifle recoil system, and should be running a buffer that's 5.4oz, and 5.200" long.  Doesn't seem like much, but the 4.8oz buffer is way too light.

Barrel details will need to be addressed.  This isn't a DPMS LR-308 factory gun we're dealing with here - it's an 80% build, and ALL the details on all the other parts need to get spilled.

The recoil spring sucks, by description of dimensions.  Just buy a real Armalite AR-10 Recoil Spring, Part # EA1095, and that will solve your spring issues, forever.

This also need to be addressed - this is your first post here, in 2019:

 

[Bill Eckberg]

Ok let me clarify the not cycling. I mean the BCG does not travel rearward enough to expel the spent shell case. I have purchased a high quality steel magazine and I can manually pull the charging handle back and get the bolt to lock back. I have put at least 100 rounds through the barrel trying to fix the ( cycling issue ) to no avail. The gun can shoot very well with single rounds. It's the part where the BCG moves back where the problem lays. Since I bought all the parts for this gun I have only done the following changed the BCG to a DPMS type. I purchased the wrong BCG. I installed a flash suppressor which made things worse no BCG movement at all. Then I purchased magpol 10 round steel magazines that have improved the bolt catch and manual BCG lock open. As of now the suppressor is removed. I have not fired the gun since doing that. I posted the parts that make up the buffer system. I have suspected that the spring is too long. I have not given thought to buffer being too light. I can understand that part. I have solved so many issues only to have the next problem rear up. Don't get me wrong even though this build has been a royal pain the azz I have learned a lot. I believe that I am missing a vital function. That's why I'm asking for help. I have so much research that I'm swimming in denile. So those that have gone through this can understand. My questions on buffer weight and proper spring length are simple. But there are so many choices. That where I need advice. So I have what appears to be the correct length buffer at 5.2" but the weight is too light. What weight is good? The spring is too long I have heard I should be using a 28-29 coil length. Someone mention the AR308 spring what are the specs? I suppose I can look that up. 

[DNP]

The flash suppressor should have little to no involvement on the gas system. Not sure how this changed anything for you in that regards. Again, check the tube, get rid of that adjustable block and out a cheap fixed block on to test it. As mentioned, your recoil system will need to be hashed out.  I’ll look to your other thread to see if there are more clauses in there, but if you can find the “water boarding” thread...that’s a great place to start so you get the idea of what folks are after. 

[98Z5V]

1 hour ago, Bill Eckberg said:

Ok let me clarify the not cycling. I mean the BCG does not travel rearward enough to expel the spent shell case. I have purchased a high quality steel magazine and I can manually pull the charging handle back and get the bolt to lock back. I have put at least 100 rounds through the barrel trying to fix the ( cycling issue ) to no avail. The gun can shoot very well with single rounds. It's the part where the BCG moves back where the problem lays.

Your gas port is too small - even for that lightass buffer.  Period.  You don't have enough gas flow.  Go back to your first post on this one, where you stated (generically) "Adjustable gas block." 

OPEN that asjustable gas block up WIDE OPEN.  All the way, until you cannot "Wide-Open" it anymore...

2 hours ago, 98Z5V said:

Barrel details will need to be addressed.  This isn't a DPMS LR-308 factory gun we're dealing with here - it's an 80% build, and ALL the details on all the other parts need to get spilled.

Next is this - not only ALL THE GUN DETAILS...   Everything that you know about that barrel, it's configuration - that needs detailed explanation.

Read this thread:

 

We can treat this like "extracting teeth" and torture - or YOU can come forward with the build details of your gun.

I can guarantee you one thing - we'll quickly tire of trying to get details out of you.  Fast.  You can front the info, or be on your own in this venture. 

Edited June 2, 2021 by 98Z5V

[edgecrusher]

1. Magpul (correct spelling for the brand) doesn’t make a steel magazine. Magpol isn’t a known brand at all and may be a different issue altogether.

2. Your spring is too short, not too long, so that’s something else. 
3. Yes, your buffer is too light. 5.4 oz is the minimum correct weight. 
4. I’m inclined to believe you have tolerance stacking issues with your receivers after reading your first post on this build.

 

 

None of this matters without more information and pictures of the build

[Bill Eckberg]

To edgecrusher

first thank you for the spelling correction on the magpul. I have a steel magazine made by C products. There is a difference between the plastic and steel. Here's what I know the tab that would be on the spring plate is different meaning the new msg engages the BCG lock correctly by lifting it into position better as observed. 

you mentioned the buffer spring is too short but don't say what is the proper length, you mention the buffer is to light I agree. 
than you mention tolerance stacking issue. So the first BCG was the wrong one meaning it was for the AR308 platform and yes that tolerance was different so I purchased a new BCG that was inspected and measurements taken to verify if there was any difference. Yes the new BCG has one quality different in that the machining looks finished in that it is smoother. The first BCG has a very rough machined surface. I believe that the new BCG slides back and fourth without the heavy gritty feel that the first BCG had. As for the barrel I have a 20" 1:10 twist the bore and four rifle lands,  for the gas port land it is .750" then the actual gas port diameter is .085" the gas block is a JP enterprises one with a standard rifle length tube for the 20" barrel. Thinking that the system was under gassed I open the block up wide open. Still the BCG is not moving. My conclusion not enough gas is being fed to the system. I will remove the adjustable gas block and use the original solid block to eliminate that problem. Hell for all I know the current block could be junk. As for the actual barrel gas port I thought during my research most gas ports where in the .055-.080 size the current port being .085 seemed to be spot on. I have checked to make sure the tube is not split and leaking. As for the tube length and engaging the BCG correctly I can only go off of the fact it was part of the original purchased upper assy. 
I have even suspected that chamber might not be finished to the correct size since the spent shells don't extract properly. Meaning it takes some extra force to clear them. I have compared the spent shell cases to another guns spent cases and mine seem to be undersized. I do reload and use calipers to verify what I'm talking about. The gun has never cycled the BCG  back and fourth properly. As for the lower assy. It is a DPMS 80% type that I finished myself. It contains a inner working for the LR308 platform. The hammer is intact with no unusual marking like the BCG gouging or marring the surface. One thing that has showed up is the buffer retention pin got bent forward towards the BCG. I suspect at one point the system was driven back so hard that the damage to pin occurred. No proof I just suspect it. As I mentioned before the gun shoots one round very well and accurate. That is as much information that I have and can remember. Pictures included. I'm not trying to be difficult about this thread I'm hesitant to give out to much info. because big brother could be watching

[DNP]

what brand is the barrel?
 

When you remove that gas block, look at the gas port and you should see a carbon ring around it. This will tell you if the block was centered over the hole. If it’s not moving at all, I think you have an issue between the gas block or the gas tube. Take a picture of the inside of the upper. Similar to the one above in the link to the water boarding thread. Where does your gas tube land in the upper?  It helps to have all the details you can spare.  

If I read your post right, it did not move with either BCG you’ve had in there, correct?  So we can probably rule it out. Chamber could be an issue, but I’m leaning towards ruling out the gas system first. 
 

 

[Bill Eckberg]

DNP don't have the build sheet available for the barrel. Let me take apart the upper and check the current gas block for the carbon ring and check the gas tube position in the upper

[edgecrusher]

Here’s what your spring and buffer should be

[edgecrusher]

As for the big brother thing lol, I’m pretty sure unless your moving large amounts of guns illegally finishing an 80% isn’t exactly on the big radar

[Bill Eckberg]

Ok here we go I got the bugger disassembled. I found the following. After removing the roll pin that holds the gas tube in the gas block the tube can travel rearward .5" to contact the BCG gas tube receiver. I have provided photos that show, how far the pinned gas tube protrudes into the chamber area. The gas tube is 15.1" in length. After removing the gas block the carbon ring appears to be centered. As for the barrel I included a photo of manufacturers logo if that any help

[98Z5V]

8 hours ago, Bill Eckberg said:

 As for the barrel I have a 20" 1:10 twist the bore and four rifle lands,  for the gas port land it is .750" then the actual gas port diameter is .085" the gas block is a JP enterprises one with a standard rifle length tube for the 20" barrel. Thinking that the system was under gassed I open the block up wide open. Still the BCG is not moving. My conclusion not enough gas is being fed to the system. I will remove the adjustable gas block and use the original solid block to eliminate that problem. Hell for all I know the current block could be junk. As for the actual barrel gas port I thought during my research most gas ports where in the .055-.080 size the current port being .085 seemed to be spot on.

 

Your gas port is too small, and I stated that without know the gas port diameter, just from your description of the function of the rifle.

A .308AR gas gun (firing .308 Winchester ammo) 20" rifle-gas barrel with a 0.750" gas block journal size needs a gas port diameter in the range of 0..093"~0.096". 

Your gun is never going to run right, until you drill that to something between 0.093"~0.096".  All barrels are not made the same - as you state, you have a 4-groove - so that's why there's a range, and not an exact diameter.  Something inside of that range will make your gun run, as fas as gas system goes.  You need to address the recoil spring, and the buffer weight, because this is a balanced system - they BOTH have to work together. 

All other functioning issues, after solving these items, will NOT be a gas system issue, or a recoil system issue. 

[98Z5V]

9 minutes ago, Bill Eckberg said:

Ok here we go I got the bugger disassembled. I found the following. After removing the roll pin that holds the gas tube in the gas block the tube can travel rearward .5" to contact the BCG gas tube receiver. I have provided photos that show, how far the pinned gas tube protrudes into the chamber area. The gas tube is 15.1" in length. After removing the gas block the carbon ring appears to be centered. As for the barrel I included a photo of manufacturers logo if that any help

 

That gas tube is WAY TOO SHORT.  You need to remove it and measure it, and it's probably an AR15 rifle gas tube.  You need to put a Real Armalite AR-10 RIfle gas tube in it.

They're longer.

Edited June 3, 2021 by 98Z5V

[98Z5V]

There's all kinds of shiit going on with this gun...   I'm just sayin'... 

[Black_Sheep]

Enlarging the gas port by .010 doesn't sound like a lot but it made all the difference in how my build ran.