DPMS LR308 compatable with AR10 barrel/bolt?

LongArm

LongArm

Problem Solver
Full Member
Minuteman
Apr 30, 2007
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Corpus Christi, Texas
#1
Here is My question. I have a DPMS LR308 ORC. I just ordered a Lothar walthar barrel (varmint Tactical) with armalite extension (AR10) and a head spaced bolt (AR10). The machinist at LW said that it is ok to run the DPMS BCG with the head spaced AR10 bolt.

Does this sound correct? In theory it seems like it will. I know some have done it. I need to know if it'll work with the ar10 barrel running an ar10 bolt in the DPMS BCG. I do not want or know where to find a AR10 BCG.
 
#4
My (limited) understanding is that with your matched AR10 bolt and extension, a DPMS carrier will work.

If it were me, I'd assemble it and just use go-no go head space gauges to see if it was within spec.

Hope this helps.

Edit to add, if the barrel has the AR10 gas tube port, you may need to use the longer AR10 gas tube. If your using the DPMS BC, use DPMS recoil spring and buffer setup to prevent damage to the lower from BCG overtravel.
 
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#5
I have put an armalite barrell on a DPMS upper and used a DPMs bolt.Headspaced and ran fine.Dont know about changing bolts out in a DPMS carrier.Goggle interchangability between Armalite and DPMs.There is a chart out there.Sorry i could not nail it down for you.
 
#6
This will work. I have seen rifles come through our shop here in cali that use the armalite extensions and bolts with dpms carriers. when switching carriers the OAL can be different, but in your case the DPMS carriers will fit your DPMS recievers and the headspace will clear.
 
#8
The Armalite AR10 bolt will work with a DPMS extension, as they are dimensionally the same. The Armalite bolt was designed to work with the Armalite AR10 bolt carrier, which has a spring-loaded firing pin to prevent slam-fires.

Both Armalite and DPMS bolt carrier groups will fit in each other's upper receivers, and interact with the barrel extensions just fine. The Armalite firing pin is totally different than a DPMS firing pin, since it is spring-loaded, and the dimensions for the Armalite carrier internally that allow for the firing pin spring are different.

I think you need an Armalite firing pin for the Armalite bolt. Check out this thread to answer your question:

http://www.ar15.com/archive/topic.html?b=3&f=121&t=473900
 
#10
The same thing I posted in the other thread:

Quote Originally Posted by usmc5593 View Post
ok, bringing this back from the dead again. I am not sure what is wrong with the "new website" but the search function and the links when searching the web are not connected??????????

Her is My question. I have a dpms LR308 ORC. I just ordered a Lothar walthar barrel with armalite extesion (AR10) and a headspaced bolt (AR10). The machinist at LW said that it is ok to run the DPMS BCG with the headspaced AR10 bolt.

Does this sound correct?
This is NOT what I was told when I bought a new barrel for my Armalite. I put the poor guy through the ringer and here is what he replied:

-DPMS barrel extension, DPMS BCA, Armalite receiver

-DPMS barrel extension, Armalite BCA, Armalite rcvr.

-DPMS barrel ext., Armalite BCA, Armalite rcvr

-Armalite barrel ext, DPMS BCA, DPMS rcvr

Armalite barrel, Armalite BCA, DPMS rcvr



You can not swap the bolts between the two carriers is the only combination that will not work. I’ve tested them all.

There are supposed to be dimensional differences between the two bolts. The tail of the DPMS bolt is longer. I can also tell you that you will have problems with gas blocks and tubes depending what gas system you have. An Armalite mid-length gas system is proprietary, DPMS .308 middy uses AR15 middy gas tube. Rifle length gas systems are the same IIRC. My new barrel which is a middy had the gas port and shoulder set for DPMS, therefore using the Armalite carbine gas block and tube wouldn't work. The tube is too long and hits the key well before the block hits the shoulder on the barrel. And my Armalite FF tube is slightly longer so I had to open it up to use the adjustable gas block I ended buying.

I think I would look for an Armalite carrier.
 
#11
Ok, I will have a LR308 with a Lothar Walthar varmint tactical barrel. The barrel will have an armalite barrel extension and will be the armalite rifle gas length. The barrel will come with a matched Armalite bolt.

So my rifle will be an armalite rifle length. If I inderstood you correctly I can use a DPMS rifle gas tube. Just so i am clear have you tested the armalite bolt in a DPMS bcg?
 
#12
I am not the person that tested the combinations. The person I bought an 18" Rock Creek barrel from sent me that info in an email. I copied that info into my posts. These are the last of his words:

You can not swap the bolts between the two carriers is the only combination that will not work. I’ve tested them all.

So what I have been told is that if you have an Armalite bolt, you need an Armalite carrier. Maybe some people have gotten away with running an Armalite bolt in a DPMS carrier, but I'm not sure that it will work and as you see, the info I was given suggest NO.

If I had a DPMS carrier to test it for you I would. I'm not sure what to say about the firing pin. I would think the
DPMS would be longer than the Armalite. I would think there are dimensional differences between the two carriers. Personally, I have swapped complete BCAs between a DPMS and Armalite rifles. I did not check the headspace but they do cycle empty which echoes the info I was given by the person that sold me the barrel.

Yes, I think you will be fine using the DPMS gas tube. You didn't mention what gas block you will use.

Now I'm going to say this PUBLICLY on this forum. When I got my new barrel I also ordered a JP Enterprises low mass .308 complete carrier and bolt. Therefore, if you want to test this, I will send you my Armalite carrier to test with. With the understanding that we both know the definitions of LOAN, BORROW, GIVE, STEAL. You can borrow my carrier and if it headspaces correctly or functions for you then use it until you can buy one and SHIP ME BACK MINE.
 
#13
usmc5593 said:
Ok, I will have a LR308 with a Lothar Walthar varmint tactical barrel. The barrel will have an armalite barrel extension and will be the armalite rifle gas length. The barrel will come with a matched Armalite bolt.

So my rifle will be an armalite rifle length. If I inderstood you correctly I can use a DPMS rifle gas tube. Just so i am clear have you tested the armalite bolt in a DPMS bcg?
Click to expand...

It is my understand that a DPMS bolt will headspace properly with an armalite barrel so if your current dpms bolt headspaces with this barrel you have on order you should be fine. That is straight from an Armalite tech I spoke with about this awhile ago.
 
#14
Ok, I have not received the barrel yet. I have a DPMS BCG. I will have to check it when it arrives. I do not like the thought of buying a armalite BCG. Parts were hard enough to find before all of this. Thanks fngmike for the offer, I may have to take you up on it. I will know more when the barrel and bolt arrives.
 
#15
OK got the "Var-Tac barrel from LW and the matched bolt that came with it. I looked the bolt over carefully and then took my LR308 apart. When I looked at that bolt they measured with in a couple thousands coal. The firing pin protrusion was .002" longer on the LR308. Both bolts had the exact same markings on them!!! A "D" and a "3". Both bolts looked the same and were within .002" coal.

I pulled out the LR308 bolt and placed the new bolt in the carrier and it went snugly in. :eek:
 
#17
The Armalite AR10 uses a longer rifle-length gas tube. The DPMS LR-308/AP4 uses a standard AR15 rifle-length gas tube. Armalite did that because the AR10 barrel nut is larger and longer than an AR15, and they are one of the few who used M16A2 handguards with their non-floated rifle-length AR10's. The Delta ring is also much larger/longer, so the rifle-length M16A2 handguards get pushed further forward, requiring the gas block/FSB to be mounted more forward, so the gas tube needed to be longer.

DPMS has not offered a rifle-length gun with M16A2 handguards that I have ever seen, as the LR-308 was always floated.
 
#19
Confusing, I am going to attempt to build a DPMS barrel, - midlength AR gas system, with DPMS extension DPMS bolt - JP enhanced bolt, DPMS upper receiver, and Armalite Bolt Carrier Armalite firing pin and spring. Only answer to a question I could not find on the net is if there is a difference between the two systems cam pins? I have head spaced gauges so I can check this before firing but it is supposed to work. The Armalite carrier has serrations for the forward assist, supposed to drag less on the magazine, less prone to slam fire but could require a heavy trigger hammer to reliably work with all types of ammo/primers.
 
#20
This gets even more involved when you start talking extension tubes buffer springs and buffers. I have and like the Vltor A5 extension which are similar or the same to Armalite AR10 extension. It should work with an Armalite AR10 carbine spring with Armalite AR10 buffer or AR15 H3 buffer
 
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#21
CSAR FE said:
You can only use DPMS spec bolts with DPMS spec barrel extensions, and AR10 spec bolts with AR10 spec barrel extensions. When it comes to .308 pattern ARs, they don't share as many interchangeable parts like the AR-15 does. It doesn't matter what carrier you use, as long as the bolt and bolt extension are made to the same manufacturer's specs as I stated above.

So in a word, yes, your machinist was correct.
Click to expand...

Sorry but you are wrong. Both DPMS and Armalite bolts have the same dimensions as far as extensions and headspace is concerned we been interchanging them for about 10 years.
The guy above you has it right, Armalite bolt in an Armalite carrier with Armalite firing pin and firing pin spring.
 
#22
bustin said:
Sorry but you are wrong. Both DPMS and Armalite bolts have the same dimensions as far as extensions and headspace is concerned we been interchanging them for about 10 years.
The guy above you has it right, Armalite bolt in an Armalite carrier with Armalite firing pin and firing pin spring.
Click to expand...
Do you know why my new Armalite bolt has the same markings (D,3) on it as does my old DPMS. The barrel came straight from LW and supposedly has a Armalite extension on it with matched bolt.
 
#23
ok, so I took out the DPMS out to shoot today. It functioned fine and was able to lock the bcg back on the last round which tells me that it is getting enough gas pressure. I say this because I used a DPMS rifle length gas tube on the Armalite rifle length system (armalite is supposed to be longer). The brass fell right at about 4:30 where they should. When I installed my can the brass fell at 1:00 as expected with the extra gas pressure.

So to recap what I have

Bushmaster ORC (DPMS built)
Lothar Walther VarTac (Varmint Tactical) rifle length Armalite gas sys, in .308 1/10 twist 20" long
Matched Armalite bolt (has the exact same markings as my DPMS bolt and is almost exactly the same size
DPMS bolt carrier
DPMS rifle length gas tube (1/4" shorter than Armalite)
PRI .875" gas block non adjustable
Troy extreme tube 13.8"
MagPul UBR
Bushnell Elite HDMR H59 3.5-21x50
AAD 34mm Mount


The rifle functioned fine with a DPMS BCG armalite bolt. It is odd that the bolt that was supposed to be a Armalite has the same markings as my DPMS. Makes me think the bolts are either the same or it is a DPMS bolt matched to an Armalite barrel extension. Either way it worked fine.
 
#24
LongArm said:
Do you know why my new Armalite bolt has the same markings (D,3) on it as does my old DPMS. The barrel came straight from LW and supposedly has a Armalite extension on it with matched bolt.
Click to expand...
I do not know unless the same company is making bolts for both DPMS and Armalite now. Or LW is selling DPMS bolts with their barrels, you would need to ask Woody at LW about that.
 
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