AR10 build help

[BERGA]

I just installed a lilja AR10 barrel in .260 on my AR10T
The barrel extension is said to be DPMS type and will headspace
with all known bolts other than KAC. Well mine is not working.
Iam having FTF's(bullet tips smashing into barrel shank) and the bolt appears to open too early, unless I shut the gas off.
I read that armalite has to use the armalite extension and most of the other bolts use the DPMS type.
Can I take a JP bolt and put it in my BCG ?
Should I take the extension off my AR10T barrel and replace the DPMS type ?
Can I get a DPMS BCG and use it in my AR10 upper ?
Would any of these work ?

 

[bmk]

Re: AR10 build help

You have a problem, but of course you already knew that. Lilja says their barrel is DPMS type, which is correct. The other type is Armalite.

Dpms type would include DPMS, Mega, Black Rain, SI Defence, and perhaps others.

Armalite type would include Armalite, LaRue, Noveske.

While some mixing and matching is allowed, generally, if you have a DPMS barrel, you should run a DPMS bolt. Armalite barrel, and you should run an armalite bolt.

My advice would be to get rid of the Lilja barrel, and get one that is set up for the Armalite pattern. I believe Noveske barrels are Armalite pattern barrels.

 

[rg1911]

Re: AR10 build help

Since I'm having a rifle built on an Armalite AR-10 lower, and because a number of parts are on backorder at Armalite, I checked with both Armalite and DPMS to ask about parts interchangeability.

The short answer is that nothing in the upper receiver area can be swapped between the two types. And uppers from one will not work on the lowers of the other.

I think that if I had not had the AR-10 lower receiver kicking around in a drawer for the past four years, I would have built the rifle on a DPMS platform, simply because parts seem to be less expensive and more available.

Richard

 

[Bennybone]

Re: AR10 build help

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bmk</div><div class="ubbcode-body">
My advice would be to get rid of the Lilja barrel, and get one that is set up for the Armalite pattern. I believe Noveske barrels are Armalite pattern barrels.
</div></div>

Do this ^^^

 

[BERGA]

Re: AR10 build help

I was wondering how Lilja could make a barrel extension that would work with all known bolts other than Knights. I read that it is GTG when DPMS pattern extension is used with DPMS pattern BCG in a Armalite Upper is this total crap ?

 

[Bennybone]

Re: AR10 build help

Each gun is unique, which is why people always post YMMV when they talk in forums.

What I've learned is Mil-spec isn't really a reality in the civilian AR industry and parts may be advertised to work but may/will require tuning and tweaking to function correctly.

Your mixing platforms and seeing the above play out.

BB

 

[Mike_in_FL]

Re: AR10 build help

I bought a Rock Creek barrel from D9 Firearms and had many an email conversation with Darrel who I believe is the owner. He told me the barrel extensions are the same. You can use whatever barrel with whatever receiver. You can mix and match whatever EXCEPT you cannot mix the bolts and the carriers. The tail of the DPMS bolt is longer than the Armalite. Armalite bolt, Armalite carrier. DPMS bolt, DPMS carrier.

Does the gun headspace correctly? You're losing me by saying the bullets are hitting the "barrel shank". What's that? They're hitting some part of the barrel extension or what? That could simply be the angle of the rounds trying to enter the chamber from the mag maybe.

What gas system length? I will tell you this and I KNOW it to be fact from painful experience. A mid-length DPMS gas system is NOT the same as an Armalite mid-length system when it comes to .308s. The gas port and shoulder for the block are in different positions. DPMS uses an AR15 mid-length gas tube and Armalite uses a proprietary length.

I am NOT sure if that holds true for the rifle length gas system. Whose gas tube are you using (brand) and what length is it? It sounds like the tube may be too long.

You can use the JP bolt but it is DPMS type. So you're going to have to use either their carrier or a DPMS carrier with that bolt. I'm running the JP low mass carrier and bolt in my Armalite upper with the Rock Creek barrel.

 

[LoneWolfUSMC]

Re: AR10 build help

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">Iam having FTF's(bullet tips smashing into barrel shank)</div></div>

Do you mean the extension (gear teeth looking thing with the feed ramps in it) or do you mean the breech face (part around the chamber, inside the extension).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">and the bolt appears to open too early, unless I shut the gas off.</div></div>

How are you determining that it's opening early?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">I read that armalite has to use the armalite extension and most of the other bolts use the DPMS type.</div></div>

Not necessarily.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">Can I take a JP bolt and put it in my BCG ?</div></div>

JP specifically recommends not doing this. I have not measured a JP bolt compared to my Armalite bolt so I can't say for sure.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">Should I take the extension off my AR10T barrel and replace the DPMS type ?</div></div>

Can't really do that. There is no assurance that the gas port would line up or the chamber would head space correctly.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">Can I get a DPMS BCG and use it in my AR10 upper ?</div></div>

Possibly, but without knowing the problem you are just throwing parts at it.

 

[BERGA]

Re: AR10 build help

The feed issue is on the breach face. This was never an issue with the factory AR .260 barrel. Even with a crimp the COL is getting set back .020 or more after feeding the round.
The gas system is rifle length and the tube is an Armalite AR10 tube installed on the JP low profile adj. block.
I thought the bolt was opening early because the cases are black all down the side, on some clear to the rim.

Since my post a have determined that my gas rings are worn,bolt won't support the carrier's weight, So that could be a leakage issue, but then I would/should be short stroking.
I did fire a round with the gas turned off and the brass came out clean.

Would the DPMS type extension cause the feed issue ? should I try to "tune" the mag feed lips ?

I can't thank you guys enough for the help and input. I want like hell for this barrel to work. I emailed Lilja, I'm sure he will stand by what he sells. I have a couple of his tubes on my bolt rifles and they are winners.

 

[Mike_in_FL]

Re: AR10 build help

Do you have Stoney Point/Hornady COAL tool? IIRC, .260 COAL is 2.790 with a lot of bullets. I'm just wondering if you're getting set back due to a short throat. There would be no sense putting a long throat on a mag fed rifle. I would ask Lilja about the M4 feed ramps or not. You could make up some dummy rounds and just slingshot them into the chamber to see if they set back or are hitting.

I don't believe this and the lack of ramp cuts on the upper would cause the problem 100%. I think it could be a lack of carrier speed and possibly needing to tweak the mag. I think that tube is too long so the air column in front of the bullet and immediate gas is causing the bolt to unlock too early. That's the blackened brass.

 

[LoneWolfUSMC]

Re: AR10 build help

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">The feed issue is on the breach face. This was never an issue with the factory AR .260 barrel. Even with a crimp the COL is getting set back .020 or more after feeding the round.</div></div>

If the cartridge is actually feeding, it's not hanging up. The tip of the bullet was hitting the breech then it's unlikely that you would have operation without a stoppage. Try your test with factory ammo if possible.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">
I thought the bolt was opening early because the cases are black all down the side, on some clear to the rim.</div></div>

My brass is filthy on my AR10. That is life with an autoloader. There is still gas in the barrel and gas tube under pressure when the bolt unlocks. This is the nature of the direct impingement gas system. An indicator of the bolt attempting to open too early would be damage to the case rim.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">
I did fire a round with the gas turned off and the brass came out clean.</div></div> It came out clean because with the gas system off no gas can get to the sides of the case. There is no pressure left in the system when you eject by hand, so no gas trying to rush through the chamber past the case to tarnish it.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">Would the DPMS type extension cause the feed issue ? should I try to "tune" the mag feed lips ? </div></div>

At this point it's almost impossible to tell where the issue is without actually inspecting and firing the rifle. My suggestion would be to take it to someone who is adept at diagnosing AR issues.

 

[BERGA]

Re: AR10 build help

Yes I have the stoney point and the mod .260 case I'll check that, but I would think Mag length would be plenty short enough for VLD's

 

[fredr1980]

Re: AR10 build help

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERGA</div><div class="ubbcode-body">I just installed a lilja AR10 barrel in .260 on my AR10T
The barrel extension is said to be DPMS type and will headspace
with all known bolts other than KAC. Well mine is not working.
Iam having FTF's(bullet tips smashing into barrel shank) and the bolt appears to open too early, unless I shut the gas off.
I read that armalite has to use the armalite extension and most of the other bolts use the DPMS type.
Can I take a JP bolt and put it in my BCG ?
Should I take the extension off my AR10T barrel and replace the DPMS type ?
Can I get a DPMS BCG and use it in my AR10 upper ?
Would any of these work ?
</div></div>

Did you ever get this issue resolved? I just received my AR1024 .260 Remington barrel yesterday and after function testing it with a few dummy rounds I made, the bullets mostly hang up right on the breach face... used 140gr Hornady A-max and 142gr Sierra MK and the 142's won't even feed at all both tested with Magpul and ASC magazines... The 140 A-max feed sometimes but the plastic tips on them are deformed from hitting the breach face going into the chamber. I think the barrel extension feed ramps were cut too deep on the back ends thus not giving the bullets the lift needed to clear the barrel extension. Please let me know if you resolved this as it is SUPER nice barrel and I want to go out and shoot it but don't want to have bullet setback on live rounds that will cause issues.

Fred R.

 

[delfuego]

Re: AR10 build help

I am having this exact same issue with my Lilja AR1024 barrel. I am in desperate need of some sort of advice or solution. I have a DPMS upper and bolt with brand new pmags and a Tubbs ar10 spring. The rounds slam into the breech face and hangup, this occurs when releasing the bolt carrier and during semiauto fire. It seems like they are even getting wedged in between the feed ramps instead of sliding up them. Bolt will hold open every time.

The ammo used was SW 142's w/Lapua brass.

 

[pagana]

Re: AR10 build help

Having built a few AR pattern rifles from scratch, i.e., completely custom starting from barrel blanks, it is probably possible to get your parts to function properly even though they are form different makers. First off the bolt/barrel/ and extension need to be timed correctly and the parts sized accordingly. This starts with headspace and clearance which both must be correct - headspace should be measured with a disassembled bolt and go gauge with bolt lugs and extension lugs in contact. clearance would then be the distance between the front of the bolt and the barrel measured as though you were testing headspace. This clearance should be between .001" to .002" for competition setups and will likely be found to be as much as a 1/64" or more in defensive setups. As far as the rounds striking the rear of the barrel, this may be because there is not enough of a lead in to the chamber. Remember, .260 is smaller in diameter than the .30 cal for which the components were originally designed so the rounds do not raise as quickly when leaving the mag. The lead in should be cut on a 60 degree angle and be the same diameter as the main body diameter of the bolt. Derrick Martin's book has the blueprints for this in his book. Having M4 style ramps exacerbates this problem in that caliber as the bullets are further forward before moving up and travel up a steeper angle.

 

[delfuego]

Re: AR10 build help

After talking on the phone with BERGA, we think this is a specific issue with this Lilja barrel. BERGA, FredR and myself all have the identical problem with the identical barrel. Dan Lilja is aware and is currently helping BERGA with the issue. I am going to contact him and wait to hear back from BERGA to see if his issue has been resolved.

The problem seems to me to be the angle or design of the feedramps (just my opinion). The round is not getting enough lift to clear the breach face and is slamming into the face below the chamber.

I am hopeful that it will be rectified and I can keep and use this barrel. The accuracy is excellent, but the feeding issue is unacceptable.

 

[delfuego]

I received a PM from another member, and just wanted to update this thread for future reference.

i am in the market for a lilja 260 drop in barrel for a dpms and came across your thread and it concerned me. what was the resolution to the feeding issues. did lilja change the geometry of the barrel to improve feeding and if so when

Dan Lilja fixed it for me. After speaking and emailing with BERGA we both had run into the same issue. Dan had re-profiled the breach-face for BERGA and fixed the issue. I asked that he do the same to my barrel, and sent it in to him. He applied the fix and shipped it back to me, and it hasn't had an issue with feeding again. Accuracy on the barrel is very good and overall I am pleased with the barrel and Lilja.

 

[hdbiker1]

I had got one of Dan's 260 barrels and haven't had any ftf, but I have noticed some tip damage from 123 Amax but not 120 Amax. So I seated the 123's a tad deeper and all is fine. Different profile I guess. I have noticed some bullet movement outwards on the heavies and plan on trying a factory crimp die.

I did talk with Dan about the bullet tips hitting the breech and he told me that he'd only had a few that did so. Also mentioned something about if I had any problems, he could add a shim somewhere. Luckily I didn't need it.