DPMS gen 1 build issues

[rogu 777]

First off hello , I'm not one who normally signs up for forums however I'm a bit perplexed buy an issue with a new build .Was looking for some insight on what the problem might be .

Right now the main issue is the bolt carrier group will not travel back far enough to allow the bolt catch to engage . I have been running through the forums and found some info but it's quite scattered and incomplete to my analytical mind. That being said let me explain my troubleshooting steps that I've taken so far perhaps an answer will follow.

The parts are all dpms gen 1 allegedly . The complete upper and lower are all DPMS GEN one Side charging handle with no issues. 

The first step I took was to measure the buffer tube it's a carbine buffer tube mil spec measure's at 7 inches.

The second step was to measure the so-called LR 308 buffer which measures exactly 2 1/2 inches and weighs 3.5 ounces. 

The third step was to measure the so-called LR308 Spring buffer spring that is and it measures 11 1/8 inches in length. It has 32 coils if I counted correctly ( perhaps I'm missing something on that one )

The only part that I'm positive absolutely positive is correct is the bolt catch/ spring and plunger. they are definitely 308.

After completing assembly it became quite apparent that the boat carrier group will not travel far enough to the rear to allow the bolt catch to engage and capture the bolt.

My first troubleshooting step was to measure all the parts check what specs I could find and then I begin removing items until I achieved the desired results. What I found was when I remove the spring and left the buffer in the buffer tube reassemble the rifle pull the bolt to the rear the bolt catch  would engage with a magazine  inserted in the mag well as it should. Releasing the Bolt catch and pushing on the charging handle would allow the boat to travel forward normally as it should. Reassemble everything with the spring and the boat will no longer travel to the rear and allow the bolt catch to engage. 

My question is what ARE the exact specifications for a carbine length LR308 buffer tube to me it seems they should be at the very least 7 1/4 inches in length 7 1/2 would be preferable. Yes I'm well aware that supposedly there is no mil spec or specifications on the 308DPMS pattern other than you can't mix certain ArmaLite and DPMS parts. 

I've seen mention of cutting Springs, milspec ar 15 buffers that supposedly work ???? I can tell you this I have several mil spec A.R. 15 buffer tubes and they all result with the same issue that is the buffer tube seems too short.

So what am I missing here ? 

 

[Armed Eye Doc]

Are you measuring internal or external length of the buffer tube?  It should be 7 inches internally.

[shooterrex]

Your buffer is too light weight wise.

The Armalite kit is longer w/a longer and heavier buffer.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories&Category=4eeff98b-d9a6-40fd-be6b-ab2e44ec1080

Heavy buffers.com also sells a buffer and spring that works in the 7" tubes.

https://heavybuffers.com/ar10carbine.html

[98Z5V]

On 8/13/2022 at 8:53 PM, rogu 777 said:

Right now the main issue is the bolt carrier group will not travel back far enough to allow the bolt catch to engage .

If this is the primary issue, it's the wrong buffer in there.  Probably an AR15 buffer, which are longer than .308AR buffers. 

[98Z5V]

Here's all the info you'll ever need about gas tubes, gas ports, and recoil systems:

 

[ebbiv]

On 8/13/2022 at 11:53 PM, rogu 777 said:

First off hello , I'm not one who normally signs up for forums however I'm a bit perplexed buy an issue with a new build .Was looking for some insight on what the problem might be .

Right now the main issue is the bolt carrier group will not travel back far enough to allow the bolt catch to engage . I have been running through the forums and found some info but it's quite scattered and incomplete to my analytical mind. That being said let me explain my troubleshooting steps that I've taken so far perhaps an answer will follow.

The parts are all dpms gen 1 allegedly . The complete upper and lower are all DPMS GEN one Side charging handle with no issues. 

The first step I took was to measure the buffer tube it's a carbine buffer tube mil spec measure's at 7 inches.

The second step was to measure the so-called LR 308 buffer which measures exactly 2 1/2 inches and weighs 3.5 ounces. 

The third step was to measure the so-called LR308 Spring buffer spring that is and it measures 11 1/8 inches in length. It has 32 coils if I counted correctly ( perhaps I'm missing something on that one )

The only part that I'm positive absolutely positive is correct is the bolt catch/ spring and plunger. they are definitely 308.

After completing assembly it became quite apparent that the boat carrier group will not travel far enough to the rear to allow the bolt catch to engage and capture the bolt.

My first troubleshooting step was to measure all the parts check what specs I could find and then I begin removing items until I achieved the desired results. What I found was when I remove the spring and left the buffer in the buffer tube reassemble the rifle pull the bolt to the rear the bolt catch  would engage with a magazine  inserted in the mag well as it should. Releasing the Bolt catch and pushing on the charging handle would allow the boat to travel forward normally as it should. Reassemble everything with the spring and the boat will no longer travel to the rear and allow the bolt catch to engage. 

My question is what ARE the exact specifications for a carbine length LR308 buffer tube to me it seems they should be at the very least 7 1/4 inches in length 7 1/2 would be preferable. Yes I'm well aware that supposedly there is no mil spec or specifications on the 308DPMS pattern other than you can't mix certain ArmaLite and DPMS parts. 

I've seen mention of cutting Springs, milspec ar 15 buffers that supposedly work ???? I can tell you this I have several mil spec A.R. 15 buffer tubes and they all result with the same issue that is the buffer tube seems too short.

So what am I missing here ? 

 

First off the buffer is correct but thats a rifle length spring, the spring should be 9 3/4" Get the proper spring first and see if it works, if not Put one round in the  mag and fire and even if the slide doesnt lock it should eject at 3-430ish, get me that  info and I'll know exactly what the issue is.

[98Z5V]

2 hours ago, ebbiv said:

the spring should be 9 3/4"

You are pushing bad, incorrect information out to people.  Completely.

This is the best reference you'll ever find, for correct spring dimensions.

https://heavybuffers.com/reference.html

[ebbiv]

54 minutes ago, 98Z5V said:

You are pushing bad, incorrect information out to people.  Completely.

This is the best reference you'll ever find, for correct spring dimensions.

https://heavybuffers.com/reference.html

bullpoopy, the spring is wrong fact. and 99% its oil, the 308s need a ton, and factory buffers are all you need, that  said  he puts the carbine spring in, and does the test fire,  then if it works it was the spriing, if not then its a gas issue, this is common trouble shooting.  you dont start messing with springs and buffers before ruling all else out.  its not an AR15, and if its new and even remotely dry its not going to work, It can be rough machining on the bolt.  I had this issue with a real factory new DPMS, and had gunsmiths and fellow owners who told me what to check and wow they were right so who are  you to claim my advice is wrong? do you even know where a round eject if is under or over gassed?  only a moron would run out and buy a fancy buffer when they haven't even ruled out the gas block.  and I gave him the published buffer weight and spring specs. He's obviously new to the platform so you're the one with bad info.  do you even know the difference between G1 and G2? i'm gonna bet you don't because people most confuse it with something else.

[jim3326]

[shooterrex]

This could get good.

[Matt.Cross]

On 8/25/2022 at 3:30 AM, ebbiv said:

bullpoopy, the spring is wrong fact. and 99% its oil, the 308s need a ton, and factory buffers are all you need, that  said  he puts the carbine spring in, and does the test fire,  then if it works it was the spriing, if not then its a gas issue, this is common trouble shooting.  you dont start messing with springs and buffers before ruling all else out.  its not an AR15, and if its new and even remotely dry its not going to work, It can be rough machining on the bolt.  I had this issue with a real factory new DPMS, and had gunsmiths and fellow owners who told me what to check and wow they were right so who are  you to claim my advice is wrong? do you even know where a round eject if is under or over gassed?  only a moron would run out and buy a fancy buffer when they haven't even ruled out the gas block.  and I gave him the published buffer weight and spring specs. He's obviously new to the platform so you're the one with bad info.  do you even know the difference between G1 and G2? i'm gonna bet you don't because people most confuse it with something else.

I'd advise you against tap dancing in that particular minefield.

 

 

[blue109]

That @98Z5V guy built one gun (with help from this board) and now he thinks he's an expert. Glad someone with some build experience is finally here to help get these guns running. 

 

I didn't realize lube was such an important element on this platform. Good to know. 

 

Edited August 25, 2022 by blue109

[ebbiv]

1 hour ago, Matt.Cross said:

I'd advise you against tap dancing in that particular minefield.

 

 

Really? I relayed the the exact information that fixed my issue, I don't dance in mindfields, I lay them  out, why not do a little search and tell everone that gave me the same advice to fix mine that they're wrong too.  

[ebbiv]

18 minutes ago, blue109 said:

That 98 guy built one gun (with help from this board) and now he thinks he's an expert. Glad someone with some build experience is finally here to help get these guns running. 

 

I didn't realize lube was such an important element on this platform. Good to know. 

 

I hope you're not talking about me, because I had one issue with one gun and it was factory new,  do a little search and talk poop to those that corrected my issue,  and by the way I have 3 308s and 10 15s, so blow me

[blue109]

I see you are equally skilled at reading comprehension and detecting sarcasm. This will be fun. 

[blue109]

@Matt.Cross don't you dare hit that button yet.....

[Matt.Cross]

On 8/25/2022 at 9:04 AM, blue109 said:

@Matt.Cross don't you dare hit that button yet.....

Have fun, be safe.

[blue109]

2 minutes ago, Matt.Cross said:

Have fun, be safe.

😂

[unforgiven]

3 hours ago, Matt.Cross said:

Have fun, be safe.

[Sisco]

[dpete]

13 hours ago, blue109 said:

That @98Z5V guy built one gun (with help from this board) and now he thinks he's an expert. Glad someone with some build experience is finally here to help get these guns running. 

 

I didn't realize lube was such an important element on this platform. Good to know. 

 

LOL.  OMFG!    Its getting deep in here.  I'll add my   too.

[98Z5V]

Wow...  

19 hours ago, ebbiv said:

only a moron would run out and buy a fancy buffer when they haven't even ruled out the gas block.

Gas block?  Really?  Did you see the rest of the spring info I linked to you in that chart?  I don't think you even looked at the chart, once you opened the webpage. It would surprise me if you knew what you were looking at in the first place.

16 hours ago, ebbiv said:

why not do a little search and tell everone that gave me the same advice to fix mine that they're wrong too.  

 

16 hours ago, ebbiv said:

do a little search and talk poop to those that corrected my issue,  and by the way I have 3 308s and 10 15s, so blow me

Do a little research, you say.  You have any idea how much research I've done on this in the past 12 years, and tested?

Tell those people that fixed your rifle to sign right up on here and I'll have a discussion with them - you obviously won't be the one that carries on an intelligent conversation about the details of this platform. 

[98Z5V]

19 hours ago, ebbiv said:

bullpoopy, the spring is wrong fact. and 99% its oil, the 308s need a ton, and factory buffers are all you need,

You are correct on oil - as we preach here time and time again.  For break-in.  Not for normal operation.

You are very, very INCORRECT on your spring length of 9 3/4.  So, any spring 9.3/4" is gonna work?

Factory buffers, if they're not 5.4oz, are not enough for a large-frame AR, unless it's a race gun tailored for a specific load, and only that load.  If your factory gun has anything less than a 5.4oz buffer, then other compromises were made to the gas system (first), and the rest of the recoil system (second)_ In that order.  To make the gun CHEAPER.

 

[ebbiv]

3 minutes ago, 98Z5V said:

You are correct on oil - as we preach here time and time again.  For break-in.  Not for normal operation.

You are very, very INCORRECT on your spring length of 9 3/4.  So, any spring 9.3/4" is gonna work?

Factory buffers, if they're not 5.4oz, are not enough for a large-frame AR, unless it's a race gun tailored for a specific load, and only that load.  If your factory gun has anything less than a 5.4oz buffer, then other compromises were made to the gas system (first), and the rest of the recoil system (second)_ In that order.  To make the gun CHEAPER.

 

First there is the M4 Carbine tube, and the the A1/A2/Rifle tube.  Now my gun does'nt matter because its a real DPMS , one of the couple dozen companies to think it was smart to not create a standardized version. The only DPMS means today is the rounded upper instead of the AR10s angled.  Next my spring and buffer don't matter because it proprietary, My buffer is 5.2" long, and weight 5.4oz exactly with a 12.75" 43 coil spring. One of my Clones has a Carbine stock, and mine is 3.7 ounces and and has the shorty 2.53" buffer.  They vary, and depending on the gun can run from 3 to 6 or more, but its last place too look, nobody considers anything else and if is cycling issue we gotta race out and mess with springs and buffers.  I never had an issue with a built, but my factory  gun fire one round, eject and not lock back, and everybody preached your bit, buffer, springs.  In this guys case could it be? sure as it seems based on his post it must been assembled by someone else, and may verywell have a pile of miss matched parts. 

His allegedly its a Gen 1 means he is totally unfamiliar with the format. No fault of his own, as most are.  It took me a couple of months to get it all down.  The Gen 1 and Gen 2 refer to completely different rifles, the G2 you never see and was sized down closer to an AR15, but still firing the 308.  It was to be the new standard for everybody but it didnt take off.  Next we have 3 different uppers, the High Profle at 3/16", and the later Low profile at 1/8", which simple refers to the thickness of the tab in the  charge handle slot.,  and the rare High Rise Target top which is a High profile with extra meat.  The problem in confustion is when the high/low started being called Gen 1 Gen 2 , it not, early and late,  say Gen 1 or 2 can cause serious miscomunications as they have nothing in common.

In the end my problem was some machine marks on the bolt, and the fact that it was new and very tight, I polished  it out, oiled  to death put a 100 rounds through it and done.  The most import thing  i checked and tells you  exact where and where not look for issues is the Bolt Lock Test Here the comment of those you think are stupid for some reason.. One of my first ideas like everyone else it to mess with buffers andd springs

Here is the list of comments in which theres no ment of "lets mess with the buffer"

1. If the bcg is tight in the carrier, the carrier bore might have tool marks in there.
Check that and then polish if necessary, without opening the Inner Diameter, but just smoothing out the carrier bore.
That’s a common problem, especially in that timeframe.  

2. Some general diagnostic steps for you assuming everything is cleaned and lubricated properly.

1. remove upper, remove bolt from bolt carrier, remove charging handle, insert carrier sans bolt into receiver and check that it moves freely back and forth with gravity. Reinstall upper onto lower, remove buffer and spring, reinstall charging handle with the bolt carrier sans bolt. With gravity, bolt carrier should freely move backwards and forwards into and out of the receiver extension. Inspect gas key to ensure it's secured.

2. With bolt removed, insert bolt into the barrel extension and rotate, it should rotate 360 degrees freely without binding. Inspect barrel extension for burs.

3. Parts inspections - Inspect cam pin for burs. Inspect upper receiver cam pin recess for burs. Inspect bolt gas rings for damage. Inspect firing pin - should move freely in firing pin channel (making sure it isn't bent). Inspect bolt inside bolt carrier without the cam pin or firing pin, pull and push the bolt in and out to see if it can move freely. Inspect bolt lugs for burs. Inspect bolt ejector and extractor pins to ensure they do not protrude. Inspect buffer detent for damage. Inspect buffer for damage and ensure that the roll pin that retains the buffer bumper is flush or below flush. Try to find out where it's dragging

3. This was the 2nd type of .308 AR I purchased many years ago after my first ArmaLite AR-10T. That’s the original DPMS LR-308 configuration. I remember when it catalogued, because we got one through the FFL in 2004 for a customer/friend of mine. got mine in 2007, and its extractor bent within the first few rounds. The chamber was also really tight and needed polishing, but you don’t want to polish excessively because that doesn’t help with obturation, and increases bolt thrust due to reduction in coefficient of friction of the case against the chamber walls.

4. Some general diagnostic steps for you assuming everything is cleaned and lubricated properly.

1. remove upper, remove bolt from bolt carrier, remove charging handle, insert carrier sans bolt into receiver and check that it moves freely back and forth with gravity. Reinstall upper onto lower, remove buffer and spring, reinstall charging handle with the bolt carrier sans bolt. With gravity, bolt carrier should freely move backwards and forwards into and out of the receiver extension. Inspect gas key to ensure it's secured.

2. With bolt removed, insert bolt into the barrel extension and rotate, it should rotate 360 degrees freely without binding. Inspect barrel extension for burs.

3. Parts inspections - Inspect cam pin for burs. Inspect upper receiver cam pin recess for burs. Inspect bolt gas rings for damage. Inspect firing pin - should move freely in firing pin channel (making sure it isn't bent). Inspect bolt inside bolt carrier without the cam pin or firing pin, pull and push the bolt in and out to see if it can move freely. Inspect bolt lugs for burs. Inspect bolt ejector and extractor pins to ensure they do not protrude. Inspect buffer detent for damage. Inspect buffer for damage and ensure that the roll pin that retains the buffer bumper is flush or below flush.
ry to find out where it's dragging.

As a starting point...

Do the "mag fed, one round... looking for BCG lock back" test.

After firing the single mag fed round.. and If it locks back on the empty mag... it appears to have enough gas to function.

Then we'll chase other possible issues.

FWIW... there is a good chance it needs a proper cleaning and relube be sure to clean the chamber of any storage oils.... and more break in time.

Lasty an article on the subject of buffers.

There’s a good amount of information out there online already when it comes to what buffer weights and springs you should use for AR-15s but not a whole lot of clarity when it comes to AR 10 buffer weights. Today, we aim to remedy that, and lets do the AR10 buffer weights and springs some justice.

To figure out which AR-10 buffer weight and spring combination will work best in your AR10 or LR308 rifle, you’ll have to first understand some key differences between the AR-10 and LR 308 platforms. Essentially, here are the main takeaways that you should know:

• AR10 is a term often incorrectly and interchangeably used with LR308.
• Most people actually mean LR308 when they say “AR-10”.
• Armalite 10 rifle parts are largely not interchangeable with the AR-15.
• Several LR-308 parts are universally interchangeable with the AR15.
• The shape of the two different upper receivers are different but have no functional difference.
• AR-10 refers to Armalite’s design.
• LR308 refers to the DPMS design. Sometimes also called ‘AR-308’.
• DPMS stands for Defense Procurement Manufacturing Services (company’s full name is DPMS Panther Arms).

Going forward we’ll continue to use the term ‘AR-10’ (in your head you can replace this term with ‘AR-308’ specifically because that’s what we sell) just think of “AR-10” as an overarching, caliber specific designation and not a reference to the original Armalite rifle.

ARE AR 15 AND AR 10 BUFFER SPRINGS THE SAME?

Technically, yes. All AR10 buffer springs and buffer weights are going to be able to fit in any AR-15 or LR-308 rifle. Whether they will make your rifle cycle consistently and perform reliably is a different story. That’s why there are specific buffer spring designs and various buffer weights which will work better or worse for certain length rifles. But yes, AR-15 and AR308 buffer springs specifically are the same length which makes them directly interchangeable.
You can actually run your AR10 rifle without any “AR10 buffer” and just use the spring. Only the first couple or few shots will work but the experience will not be pleasant. The violent action of the BCG going back and forth will be more intense and cause more wear and tear on your gun. There’s also no guarantee that the gun will cycle consistently.
The main difference in the AR buffer springs lies in the length. Going back to the actual AR-10 (Armalite design), the interchangeability is not reliant on whether you’re using an AR10 or AR308, it’s actually a buffer tube issue. AR15 style stocks are compatible with both AR15’s and AR10’s, hence the compatibility, because they use the same length buffer tubes. But if you use an A1/A2 style stock it will require a longer spring.

AR10 BUFFERS (LR 308) EXPLAINED

There are three types of buffers – rifle buffers, carbine buffers and adjustable buffers. So when do you use a carbine buffer vs a rifle buffer? Carbine buffers or buffers with weights that fall under the H2 or H3 category are most commonly what AR-10 owners should be using along with carbine length butt stocks. Rifle buffers are really only used with the A1/A2 style buttstocks due to the rifle buffer tube being longer. Basically every buffer used today is going to be some sort of carbine length buffer.
Why are buffer weights important? If you were to shoot with just a buffer spring and no buffer weight in a full auto/select fire AR-10 — you’d likely experience light strikes and because the timing of the bolt going back and forth would be off and not completely in sync with the hammer.

Having a buffer slows that cyclical action down to help you avoid light strikes, promote reliable cycling of rounds being fired, ejected and properly fed into the chamber. Once dialed in, you might surprise yourself with a softer and flatter shooting AR10 style rifle than you initially expected. You also don’t want too heavy of a buffer either otherwise you risk slowing down that bolt way too much which would cause malfunctions or failures.

CHOOSING AN AR10 BUFFER WEIGHT

Generally speaking, don’t get hung on the rifle length buffers. AR10 carbine buffer weights will range anywhere between 3.8 to 5.4 oz for any AR10 style rifle. But that weight range can also depend on where you’re getting the AR 10 buffer from as well. The chart above is specifically for Odin Works’ adjustable buffers which allow users to tune their buffer weight to get your AR308 rifle cycling just the way you want.
There’s no “one size fits all” answer when it comes to the topic of AR10 buffer weights and springs because there are just so many factors involved. Namely, the rifle length, ammunition load, buffer weight, buffer spring type, whether you’re shooting suppressed, etc. Some experimentation or trial and error is going to be inevitable but with this information you can make a better and more educated guess. Unlike the AR-15 buffer weights, we don’t have a chart for you based on length of rifle for AR-10s because there is less of a barrel length difference in AR10 style rifles. Most barrels are going to be around 18” to 20”.
But understanding the symptoms, like if you’re experiencing short stroking or a failure to feed or eject — will also help you know what you’re dealing with and advise your next move. Below, you’ll see a figure for how to diagnose the “health” of your rifle’s ejection angle based on which direction empty casings are flying after extraction. This concept applies to the AR-15 just the same as the AR-10 or AR-308. 

 

DON’T FORGET ABOUT THE GAS BLOCK

A lot of people seem to forget how big of an impact the gas block can have on the shooting experience of any AR platform rifle. Most factory built guns are going to come with an overgassed gas block which will promote higher reliability between different parts and a wider variety of ammunition loads.
But when you’re building your own rifle from the ground up that tends to get in the way of properly tuning your rifle. That’s why it’s highly advantageous to have an adjustable gas block as it could mean the difference of your rifle cycling or not. Still, it’s best to think about the adjustable gas block as a fine tuning process whereas the majority of your guesswork is going to be within the buffer system.

[98Z5V]

You are an idiot.

You're just copying and pasting anything you can find on the internet - yet, you're so smart, and know all this...   then why did someone else figure out your gun for you, and you're going to sick them on us...  

Read this - I wrote this myself.  Didn't copy it and paste it from around the web.

 

19 minutes ago, ebbiv said:

There are three types of buffers – rifle buffers, carbine buffers and adjustable buffers.

There are alot more than that.  Rifle buffers for AR15s, Rifle buffers for .308 ARs,  RIfle buffers for Rock River Arms LAR-8 varients, Carbine buffers that are 3.250 long, 2.500" long, and again, for Rock River Arms LAR-8 guns - do you know how long those carbine buffers are?  I do.

VLTOR A5 buffers, 9mm buffers...   the list goes on.