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>>>