I recently build an M4 type AR15 using a flattop upper from Bravo Company... It works alright but if I look up into the upper receiver the gas tube does not seem to be centered.  Will this cause any wear issues?  Is there a way to fix this or should I get another upper, or not even worry about it?

Remove the bolt from the carrier and then install the carrier into the upper receiver... With your finger, move the carrier back and forth to feel (or some times hear) if the tube hits the key or binds with it...

If the tube does bind or touch the key in any way, you will need to make an adjustment to the tube...

There are different ways to adjust the tube depending on the gas block... Is it a standard front sight or a gas block with set screws?

If its an original standard FS then you can carefully bend the tube inside of the receiver to straighten it (a flat wide blade screw driver inserted next to the tube closest to the front of the receiver and giving a twist works pretty well for side to side adjustments)... If its a gas block with set screws, you might need to slightly adjust the block, but to much will move the windage to far out of spec...

Also, make sure that the barrel nut isn't pushing it over to one side. The gas tube should go through a notch in the barrel nut without touching it.

Quoted: Also, make sure that the barrel nut isn't pushing it over to one side. The gas tube should go through a notch in the barrel nut without touching it.

+1...

Quoted: I recently build an M4 type AR15 using a flattop upper from Bravo Company... It works alright but if I look up into the upper receiver the gas tube does not seem to be centered.  Will this cause any wear issues?  Is there a way to fix this or should I get another upper, or not even worry about it?

One of my uppers from Bravo Co. had a bent gas tube and was engaging the key bad. I sent it back they replaced the gas tube. I emailed about reimbursement for return shipping and was told it was in the mail, i never got it but it was only like 8 bucks or something. They have a good rep. so i`m sure it wasn`t intentional.

Thanks guys, the barrel & gas tube are Bushy.  The FSB is the regular one.  I don't think the barrel nut is pushing on the gas tube.  

If I slide the carrier back and forth, I *can* definitely feel it when it reaches the gas tube.  

So, I think I will try slightly bending the gas tube over.  There does seem to be some "wiggle room" if I reach in and push the gas tube to the side.  Would another option be to slightly rotate the barrel nut to push the gas tube in the right direction?

Thanks for all your help guys!

Quoted: Thanks guys, the barrel & gas tube are Bushy.  The FSB is the regular one.  I don't think the barrel nut is pushing on the gas tube.   If I slide the carrier back and forth, I *can* definitely feel it when it reaches the gas tube.

That DEFINATELY sounds like the barrel nut is slightly pushing on the gas tube (been there several times).

Yes you can bend it, but in the long run you are far better off removing the tube then loosening up the nut and retorquing it so the tube has a clear shot w/o interferance.