LR 308 DPMS,, Extractor

[carbon9]

This is a great thread, let's keep it going. Funny how the Ar-.308 is such a different beast then the Ar-15. All the different avenues to end up with something reliable, maybe some consistencies will start to show over time with this thread. As soon as I load some more ammo I will deconstruct some of the changes I have made to see what the bare minimum is for this rifle. Of course, yours may be different.

[392heminut]

I have a DPMS LR308B but I haven't tried to offer any advice here because my rifle has just flat ran ever since I took it out of the box. I've put over 500 rounds through it consisting of Tula steel case ammo, Federal Match and a bunch of handloads using two different powders. This gun has never malfunctioned so it is possible to get a good reliable DPMS .308! One thing I did do was run the BCG dripping wet with oil the first 200 rounds or so to break it in. The gurus over at 308AR.com highly stressed that these guns HAVE to be run wet during break-in! If you don't get it sorted out, post up the problem over on 308AR.com and get some feedback there. There are four or five guys over there that have a huge amount of knowledge between them on dealing with issues with the .308 rifles, both the Armalite and DPMS platforms.

[M ammo]

Thanks for the new input,,, when to the range and tested what I got,,,, same same,,, FTE,,,, I'm going to play with making the buffer heavier,,, here I go!!!

[M ammo]

Ok so far,, I weighed all the buffer parts,, the factory one was about 4 OZ,, on AR 15,, someone had a thread,, that said, an 8 to 9 OZ buffer weight, was working for them,,,

SOooo after taking a wild ass guess,, I got my bullet casting pot all warmed up,, and filled it half way,, let it cool,, weighed it,, it was about,, 4 OZ,, so then I filled it up to the point that I could, put the buffer, pad back on it,, I put it back together, and when I'm at the range tomorrow doing some other range work,, I'll try test firing it again,, and hope for the best..

[Rookie]

My new out of the box (Jul-2012) LR-308 ran at near perfection for the first 350 - 400 rounds, then turned into an extraction problem beast during the 2013 SMM3G. An assessment from the gang at Accuracy speaks determined that the bolt and barrel centerlines were (apparently) not aligned. The problem descriptions at the beginning of this thread seemed to be very consistent with my experience. Accuracy has made adjustments and the rifle is back to shooting much more accurately than I can shoot it... and I can only hope that the "extraction beast" does not return for the MG Nats later this month.

Has anyone else checked to see that the bolt and barrel alignment might have been a contributing factor to their problem? It appears that in my case, the bore and barrel threads were offset.

[M ammo]

Ok back from the range,, test fire with weighted 8 OZ buffer,,,,

still not up to 3 gun standard,, BUT,,, it ran better so I'm on the right track.

I got through the first mag,,, no problems,,, second mag,,, well,, it didn't get them shot,,

same problem FTE---- the bolt would still lock back,,

a Much lighter kick,, was nice,,,

so what do I have left,, an Adj gas block,

and or more weight on the buffer,, I can make something like the tub system, if the Adj, gas block does not do it,,

in the end if the gun works,, it will not be a DPMS when I get done,,

live and learn,,, ouch!!

[co-exprs]

If all else fails... Give it to Benny and see if he can find the problem. He's in your neck of the woods, knows the platform well and is always up for a challenge.

[pyrrhic3gun]

OK, so you have the DPMS LR308 double-spring (p/n 308-bt-08) and two (not one) #1 o-rings under the extractor?

If it doesn't work with that, then I would suggest an adjustable gas block to close down the gas a little, and an Endine buffer from Brownells.

[M ammo]

It is close,,,, the adj,, gas block is on order,, I think it's doable,,,

I have to say in the 308,, the extra weight in the buffer,, is nice!!! much softer, more of a slower push,

It has been a long road on this gun,,,,, I so want it to be worth the trouble,, and more gray hair,, I got from it,

[Dan Sierpina]

Is the new barrel a rifle length gas system? Is your brass a bit oversize at the base? I found with military once fired brass, it was pretty big and needed a bit more sizing to chamber and extract properly.

[M ammo]

it is a 20 inch,,, reg gas tube,, length,, the ammo was new or small base sized,, they all fall in and out of a JP gage,, its way over gassed,,, I'm happy I have a weighted buffer now,,, I would recomend that to folks for sure,, it was easy too,,, If you have a way to melt lead,,,

[co-exprs]

Before you start doing surgery, find someone else with a 308. Swap out the Bolt carrier group and run a mag. Generally speaking a 20" with rifle length gas shouldn't be over gassing the gun, unless the hole in the barrel is oversized. But you said the FTE problem spans two different barrels. So first drop in a complete BCG from a friends 308. If good then swap out just the bolts. If the rifle works with a different BCG and with only the bolt swap, then I would agree to look at the gas. If it runs with his carrier and not with your bolt then you may have a headspace or a dimensional defect of some kind in the bolt. But that is only a guess. There is a root cause here and until you find it, you will always be chasing the symptoms and the rifle will always be unreliable.

[M ammo]

can't say I know anyone with a DPMS 308,, too swap,, parts,, I have found out that AR's in 308 are NOT,, like 223 AR's all of the parts are not interchangeable,,

, hmmm as for Surgery,,, too late,,, for that,,

the gun ran 90% so I'm on the right track, but one in every 10 rnds,, is not 3 gun ready,,,

[casanovaracing]

I just browsed this whole string and am likely just restating but... in an early post there was a line about over gassed. Fix that and polish the chamber= problem solved. If you think about the businesses of adding weight to the reciprocating parts you are adjusting for an over gasssed system (a little Newtonian Physics). I have done that with a couple DPMS 308s with great success. Good luck.

Edited April 8, 2013 by casanovaracing

[M ammo]

Well casanovaracing,,, your probably right,,, but adding lead,,to the buffer. was cheap, too, and a buffer is,, under $10,,,, I cast bullets,,, so I have lead and a way to work it,,, a gas block was $100,,, I when with the cheaper text,, ,,,,, the weight helped,, the gas block, will probably do the rest,

I'll know in a week,, after I get the part and have a chance to text it at the range,,

[M ammo]

Still having the same problem, fail to extract,, I can got a 10 shot string,, then it will not extract,,, next time it will do it on the first round,, then I can get 15 shots off,, then a FTE the only part of the gun that is now original is the bolt carrier,, stripped upper and lower,,,, I don’t have much left to change,,,

Used Factory ammo ,, hand loaded ammo,, many types of ammo,,, same problem,,

the only parts left is the bolt and carrier,, I have tried, a JP bolt in the Gun,, thanks Trapr… it did the same thing,, and I did put a longer gas tube in the gun,, a so called 308 tube,, it did not change the,, FTE issue,,

[pyrrhic3gun]

In your very first post you say you have the heavy duty spring under the extractor.

I'll ask again (because I'm a glutton for punishment) do you have the DPMS p/n 308-bt-08 spring with two (not one) #1 o-rings around it?

The heavy duty AR15 spring won't work.

Do you have the adjustable gas block on it?

[3-Gun Sweden]

I've seen broken exctractors on JP LRP-07. Same issue?

[M ammo]

In your very first post you say you have the heavy duty spring under the extractor.

I'll ask again (because I'm a glutton for punishment) do you have the DPMS p/n 308-bt-08 spring with two (not one) #1 o-rings around it?

The heavy duty AR15 spring won't work.

Do you have the adjustable gas block on it?

I put on a JP,, gas block,,, so yes,,,

I have tried, 3 different extractor springs,,, now,, and the lil black inset thing is in it,,

and I will,,, get some #1 o-rings and put in 2ea,,,,,, sounds like a good idea,,, thank you,, funny,, but once I read it,, I thought,, DAAA I should have thought of that,,

[co-exprs]

M Ammo,

Do me a favor... remove your bolt, take a casing and see how easy it is to hook the casing on the extractor. Once hooked, use the case to manually compress the ejector spring and see if the extractor holds the case rim properly.

A few weeks ago I finished up a 223 build and installed JP LMOS with brand new Enhanced bolt. I was getting some FTE's where the spent case was sometimes (about once per mag) left sitting on top of the magazine and gummed up the works. I noticed that it was harder to hook the case on the extractor with this particular bolt, than with others. I swapped the extractor and the problem was solved. I realize mine was a 223 problem an not a 308, and that you have already swapped extractors, but at least check this off your list of potential root causes. Did you ever get a chance to swap in a buddies BCG?

[M ammo]

M Ammo,

Do me a favor... remove your bolt, take a casing and see how easy it is to hook the casing on the extractor. Once hooked, use the case to manually compress the ejector spring and see if the extractor holds the case rim properly.

A few weeks ago I finished up a 223 build and installed JP LMOS with brand new Enhanced bolt. I was getting some FTE's where the spent case was sometimes (about once per mag) left sitting on top of the magazine and gummed up the works. I noticed that it was harder to hook the case on the extractor with this particular bolt, than with others. I swapped the extractor and the problem was solved. I realize mine was a 223 problem an not a 308, and that you have already swapped extractors, but at least check this off your list of potential root causes. Did you ever get a chance to swap in a buddies BCG?

I have played with the and put his JP bolt in my gun,,, hmmmmmm

I'm still waiting on an e-mail from the JP folks,,

but I'm going to play with the extractor, spring and Rubber O rings,, Hell I might just JB wield it in and see what happens,

all the ammo fall in and out of my JP case gage,,,,,,, and I can hand cycle the ammo through the gun,,,

hmmmmmm

I know I'm not the only one that has this problem,,, if i shot off a bench all the time,,, its no big deal,,,

But in 3 Gun, NOPE,,, the gun needs to run!,

[co-exprs]

Yeah this one is a real head scratcher for sure. I'm running out of ideas.

[M ammo]

Yeah this one is a real head scratcher for sure. I'm running out of ideas.

Yes,, but I appreciate your Ideas,,,

I did get an e-mail from the JP folks,, they are working on a new better extractor, but its not out yet,,

[co-exprs]

And don't get me wrong. If it runs better on a heavy buffer, then by all means run a heavy buffer. I'd just like to see us get to the root cause of the problem and learn some thing from it.

[benny hill]

I had the problem on a gun. It was overgassed. Put in a adj. gas block and set it where it would JUST back & no more problems.