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Posted: 1/3/2006 3:58:40 PM EDT

but wanted to know how hard it was to line up the gas tube and bolt with the upper reciever (I've heard that the bolt needs to be lined up for proper function)? The lower seems straightforward on assemply and all I have to do is find some of the right tools to do it. Anyexperience in this area or tips on assembly is much appericiated

Side Note: reason being that I have chnaged around my AR so much I have enough spare parts around that All I need to do is buy the Bolt , and full parts for a upper & lower receiver.
Link Posted: 1/3/2006 4:18:15 PM EDT
Lining up the gas tube is not something to worry about.

The barrel is held in place by a nut. That nut has "teeth" around the outside.
A gap in the teeth needs to line up with the hole through the upper receiver that the gas tube passes through.

You tighten the barrel nut to ~30 ft-lbs, and hopefully one of the gaps will be coming up to lining up with the hole. If not, you can tighten more (up to 80 ft-lbs) to get the next gap into line.

Once the hole gap is close to lined up, put the gas tube in place -- or you can buy a special tool (otherwise known as a bit of sawn-off gas tube) to use in its place. The, take the bolt carrier, without the bolt in place, and slide it into the upper.

Watch as the gas key (the thing on top of the carrier) engages the gas tube. You should feel only the slightest resistance as the gas tube slides into the key, and the gas tube should NOT move at all. If it moves one way or the other, watch which way it moves - you will need to tighten/loosen the barrel nut just a touch to move the tube so that it lines up with the gas key.

Once the bolt carrier slides in with minimal friction, and no gas tube movement your gas tube is aligned.

Its actually pretty easy, and also pretty intuative once you start looking at it.

The hardest part may be getting the nut "gap" to align within the torque range (30 to 80 ft-lbs), and also measuring that torque. You can try backing off the nut and re-tightening, often that will be enough. Don't get fixated on the actual torque value. The barrel doesn't have to be held all that tight to work - it just really needs to be tight enough not to come loose later. Overtightening can damage the thread on the upper, and/or distort it, so just don't go nuts and over-torque the barrel nut.
Link Posted: 1/3/2006 4:23:36 PM EDT
[Last Edit: 1/3/2006 4:27:25 PM EDT by M4Madness]

Originally Posted By Firelotus:
...but wanted to know how hard it was to line up the gas tube and bolt with the upper reciever...



It's not hard at all. To install a barrel on an upper receiver, you'll first clamp the upper inside an action block in a vise. Then apply some moly lube to the threads on the barrel nut. Then you'll screw it onto the upper by hand (no wrench). Then you'll use a barrel wrench with a torque wrench attached and torque it to 30#. Now look into the rear of your upper receiver and look through the gas tube hole to see if a notch in the barrel nut will clear the hole. If you are using a factory delta ring assembly, you'll need to take a punch and align the holes in the delta ring, snap ring, and weld spring for the gas tube to go through.

Tighten the barrel nut more if needed until the gas tube will go through one of the notches without touching the barrel nut. Push the gas tube through from INSIDE the upper as far as you can and eyeball it from above to make sure that it is parallel to the barrel, and tighten the barrel nut more if needed. Once you have a notch aligned without the gas tube touching it, pull the gas tube out and install it correctly from the front. The gas tube roll pin is the only thing holding it straight, as it should float freely through the barrel nut and receiver.

EDIT: Looks like PhilipPeake posted while I was typing.
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