Gas tube too long?

[je25ff]

So I'm finishing up my AR build. I have the barrel nut on, the gas tube in to the receiver and the A2 front post gas block. With the BCG fully forward, the gas tube pin hole on top of the gas block won't line up. If I pull the bcg back, I can get it to fit but, pushing the bcg forward pushed the gas tube too far forward. The bcg is a bravo company one and the gas tube is from a non-A2 front gas block (also bravo company). Maybe that's the issue? It's got to be maybe 1/8 of an inch, if that, out of alignment.

Edit: The gas tube is a carbine length as is the barrel.

 

[Another_David]

EDIT: just to clarify you install the gas tube and its pin THEN install the BCG. You won't be able to align the tube with the BCG forward, but otherwise:

1. Make sure you have the gas tube in the right place on the A2 post. The pin goes in the gas tube notch of course.

2. Make sure you have the right length gas tube, see these threads:

http://www.northeastshooters.com/vbulletin/build-yourself/192059-gas-tube-length-question.html

3. You might just need to align the tube:

take the upper off then remove the bolt carrier assembly. Take the bolt out of the carrier then slide the carrier in by itself. It should slide freely over the gas tube. If the tube snags the key at all then check that the key is straight, tight and staked. Then you can adjust the gas tube by bending it to be in the center of the key. one way to test, which way to bend the tube is to apply pressure to the tube where it is exposed above the barrel (with the hand guards removed)

 

[je25ff]

Awesome. Thanks, dude. I was trying to avoid having to possibly remove that dam gas block pin. I'll double check the length as well.

 

[je25ff]

So now I'm confused. The gas tube I have is 9 3/4" My only guess, again, is that it was specifically made for an A3/no front post, flat top, gas block (which doesn't match my barrel anyways, saving for next build)

 

[Another_David]

9-3/4" is the correct length for a carbine gas tube

are you sure the block is in the right place and the barrel hole, gas block, and tube hole all line up? Once together you can block the chamber end of the barrel then blow down the barrel and see if you have air pressure coming out of the tube. Helps if you hum the National Anthem while blowing.

What comes to mind first is the tube is not seated all the way in the gas block and the gas tube roll pin is inserted ahead of the tube and not through it. Insert the gas tube then put something in the hole like a small punch or a thin nail and make sure it's in the gas tube hole by trying to back out the gas tube.

Secondly, is you gas block on the right way? I think some have holes on both ends of the block and can be installed backwards, but the gas tube won't line up with the barrel hole, etc.

else, something is out of spec! (as if you didn't know that already)

take some more photos. What kind of gas block is this? How far into the upper does the gas tube protrude?

 

[je25ff]

Well, I installed the gas tube first then the bcg. Action is just fine now. Need to disassemble it and put in a hand guard retaining cap and dremel down the front sight post pins (they suck), hammer them in, and off to the range with it. Not sure why the gas tube wasn't fitting right but it appears to now, just need to make sure the head space is OK before I head to the range.