308 build

[MiltRodriguez]

Hey everyone, gotta question that is probably pretty newbie but can't figure out.

I'm doing my first build of an LR 308. I put everything together and the Bolt won't fully helix. It's a faxon barrel, mid length, 16". I have a mid length gas tube as well. Some easy questions to answer...yes the tube is aligned with upper properly, I used an alignment pin for the barrel nut/ rail adapter. Yes the barrel extension alignment pin is properly inserted in the upper. Yes I properly installed the gas tube pin through the gas block and the gas block is properly aligned. What I noticed as I took things off to check was when I pulled the gas block and tube off, the bolt went all the way forward and helixed properly. I know the length of tube is correct from what I've read.

What I did was take my BCG and put it into my buddies lr 308 build, same lower and upper, and it worked fine. After comparing, I noticed my gas tube extended about a 1/4 inch further into the upper than his. So I did some research and found that the armalite-10 gas tube is about a quarter inch longer than a DPMS LR 308 one. But the package for the gas tube says nothing about armalite length or anything, just mid length, (marked by the shop btw).

Sooo..anyone experience this or agree that it may just be an armalite gas tube?

[FaxonFirearms]

Easy to test.

Remove the gas tube and will the bolt lock into battery? If so, it could be the tube.

Do you have a photo of the barrel you could send me with the logo visible?

[Junkie]

If your tube is longer and it works when you remove it, it sure sounds like the tube is the problem.

[ar15barrels]

If you bought a gas tube that was specifically sold as being for a 308 build, it was an AR-10 gas tube.
Armalite AR-10 pattern guns use a gas tube that is about 1/4" longer than the same length (carbine, midlength or rifle) AR-15 gas tube.

LR-308 pattern guns use an AR-15 gas tube, but you need to put some additional bend into them to accommodate the gas key being higher above the bore than on an AR-15.
I am not aware of anybody that sells proper LR-308 specific gas tubes.

[MiltRodriguez]

If you bought a gas tube that was specifically sold as being for a 308 build, it was an AR-10 gas tube.
Armalite AR-10 pattern guns use a gas tube that is about 1/4" longer than the same length (carbine, midlength or rifle) AR-15 gas tube.

LR-308 pattern guns use an AR-15 gas tube, but you need to put some additional bend into them to accommodate the gas key being higher above the bore than on an AR-15.
I am not aware of anybody that sells proper LR-308 specific gas tubes.

Thank you this is very helpful. It was an lbe unlimited gas tube. It had an additional sticker on it, (I don't know if it was the shop I bought it from or lbe unlimited) that said 308.

[MiltRodriguez]

Easy to test.

Remove the gas tube and will the bolt lock into battery? If so, it could be the tube.

Do you have a photo of the barrel you could send me with the logo visible?

Should've clarified, but it's definitely not the barrel. BCG locks fine into to battery without the tube. Thanks though!

[MiltRodriguez]

If you bought a gas tube that was specifically sold as being for a 308 build, it was an AR-10 gas tube.
Armalite AR-10 pattern guns use a gas tube that is about 1/4" longer than the same length (carbine, midlength or rifle) AR-15 gas tube.

LR-308 pattern guns use an AR-15 gas tube, but you need to put some additional bend into them to accommodate the gas key being higher above the bore than on an AR-15.
I am not aware of anybody that sells proper LR-308 specific gas tubes.

Also where would I actually make this bend...I haven't been told this step in a build or even seen it.

[ar15barrels]

Also where would I actually make this bend...I haven't been told this step in a build or even seen it.

Just increase the bends that are already there until you get the extra height that you need for the gas tube to go straight into the receiver.

[gemini1]

Hi Randall. Is it a must that the tube be bended more? I didn't do that when I installed my GB/tube, and it was aligned at the receiver hole. The rifle has functioned well after 200 rounds, and I dont see any scratch marks on the tube end that goes in the gas key.

[ar15barrels]

Hi Randall. Is it a must that the tube be bended more?

Only if you want the gas tube to last a long time.
It will simply wear out faster if it does not align properly.
Most people don't shoot their rifles enough for it to be a problem so you don't hear much about it.