Fishco

Well as I expected the 16" & 20" barrels that I have, which are both stamped DPMS are machined wrong! I just got my buddys new barrel today, straight from DPMS and there is clearly about 5/16" diffrence in the location of the gas port due to incorrect machining of the barrel. I will post pictures and measurements later. Got barrel set in my lathe and I am turning it to correct specs!

Jgun, Thanks for the idea, but I want to be able to swap out parts without altering them, if the barrel is the problem(And I am sure of it now) I just fix the barrel and then all standard tubes, gas blocks will all work, without fitting them. I have tons of parts and I want to be able to go to a drawer and just pick up a part and slap it in. On the side of caution, I am checking one more thing, one of my other fellow builders in my area has a DPMS 16" carbine barrel on order from DPMS, I am going to compare it to his when it comes in next week. I will take pictures and post the results!

Jgun, From the end of the barrel extension to the end of the barrel where the gas block butts against it I have: 13 9/16".................from the stop lip of the barrel extension that butts against the reciever.....12 5/16" .................. from the back of the stop lip on the barrel extension away from the reciever..12 3/16" At this point I don't think I have anythiing to lose in turning this barrel back 5/16", it doesn't work now....

The next gun build I do, I am going to measure and spec out every single piece that I can, so to help the next poor guy like me! I could get my 14 year old to build an AR platform rifle with his eyes closed, but this one has stumpted us.....We built it and it didn't work :-( What should have been lees than a one hour build, has turned into a week process, oh well at least I will learn from it!

jGun, Not cutting yet, was going to start this afternoon, do you have a measurement from the end of the barrel extension to where the gas block butts up to where the barrel is turned down, or to the gas port hole.

I think that who ever made these barrels did not allow for the diffrence of the bareel extension, I think they were in AR-15 mode and should have been in LR-308 mode... Have no fear, I will trim the barrel back and re-install and test. I will be back in a few days and post the results, wish me luck!

Jgun.... Yes, Rifle, Rifle, Yes........I have positively confirmed its the barrels, they are off 5/16"....

If you go back and view the first pictures I posted, of the under sider of the upper with the gas tube installed, and compare that to the last pictures I posted or the barrel coparison, the diffrence, would suggest that the barrels are not correct. I am going to turn an additional 5/16" from the barrel where the gas block mounts, re-drill the gas port hole and re-assemble and test fire.....

Man I don't know anymore....Barrels are stamped DPMS

Here is an update, I have removed an AR-15 rifle length barrel and compared to the rifle length LR-308 barrel. There is 5/16 inch diffrence, from gas balock location to end of barrel where it mounts in the upper. I think I have been sold "second's" barrels, not only a 20" but also a 16", what are the odds, only me. I have attached pictures, the barrel on the left is the .223-5.56 and the one on the right is the .308-7.62.

Ok I have now ruled out the: 1: Gas tube 2: Gas Block 3: Barrel extension 4: Upper Receiver I am leaning toward not 1 but 2 incorrect machined barrels... Does anyone have a DPMS 16" and 20" barrel not mounted that could give me some measurements or direct me in the right direction to find these? I am getting nothing out of DPMS..

I will be posting back my findings once I take apart the non working gun and one that works... Hang in there, we are going to solve this mystery!

This is what I know so far: 1: Tried several gas blocks, roll pin location is correct, not on backwards, can blow through gas tube and air passes through. 2: Checked and re-checked several gas tubes and are passing air test and all are correct lenght 3: All parts are direct from DPMS 4: Tried 2 diffrent DPMS Barrels, a 16" and a 20" and still have same problem. So it has to be 1 of 3 things: 1: Both barrels have in-correct located gas block mounting area 2: Both barrels have in-correct barrel extensions I highly doubt that 1 or 2 is the case or 3: Upper is machined in-correctly I am leaning on the upper being defective. I will disassemble on of my workin guns tonight and compare. I will add more photos. Thanks for all the input, please keep it coming, I need help to solve the puzzle!

Upper came straight from DPMS......Man I am at a loss. goint to completely break down one of my others and compare upper to upper...

Heck, theres only to possibilities, the barrel extension is too long or the front sight/gas block is located to far forward. Funny its the same on 2 barrels.... I don't know, you would think I could send this to DPMS, but they said since they din't assemble the gun, NO CAN DO>>>

Correction barrel extension.....

Yes, everything thing is drilled correctly... I just notiiced that when I compare it to other guns I have it seems that maybe the barrell nut is too long? Is this possible???

Everything seems to be in the right spot. Hole looks to be correct, its the same problem on the 16" & 20" barrells on this particular upper.

I am starting to think the reciever is defective, maybe where the nut jams against the barrell, possible too long of reciever?

I have new gas tubes ordered, but the one installed is the correct lenght......

I have built 4 DPMS lr-308 rifle and my last one has me baffled! The problem is that it won't cycle a round and load another, hold on, its not a magazine problem. You can manually cycle rounds and emptys through the magazine and no problem. When I fire it, the bolt comes back about 1/2-3/4 inch and thats it, you can go ahead and manually cycle it out, but the gun wont do it. I have tried this with a 16" & 20" barrel and the same issue. I have tried other barrells on this lower and no problem. I have swap complete carriers and still same issue. The only thing I have found is that the gas tube doesn't come into the upper as far as my others. It is about 1/4-5/16 inch short, therefore it is not seating in the gas carrier as far as my others. I have re-torqued the barrel many times and it still wont go any deeper, changed the gas blocks and still the same. All parts are factory DPMS, they won't help me since they didn't assemble it... What the crap have I done??? Please help!