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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 8/28/2005 1:11:08 AM EDT
I've got a new 6920 upper that I've finally cleaned the grease off of to go shoot. But, as I cleaned and lubed it up, I noticed the bolt carrier group seemed to really stick before it would go all the way into the upper. So, I pulled it, removed the bolt and tried the carrier without the bolt, it also stuck. So I tunred the upper upside down to observe the carrier as I inserted it, and sure enough, the sticking point is at the gas tube/gas key interface. So, I removed the carrier and had another look into the upper and the gas tube appears to be bent to one side by about 2mm causing the hang up.

My question is, can I bend the end of the gas tube straight (and get a reliable, durable fix), or do I need to just replace it?

Thank ya'll.
Link Posted: 8/28/2005 4:07:34 AM EDT
It is somewhat common for this to happen and it depends on alot of things.

You can reach in there and tweak it around with a screw driver, if your alignment issue it side to side only - the most common BTW. Just be careful and pad the inside of the receiver, as you can ding it with the screw driver if you aren't careful.

If you have top to bottom misalignment, it gets a little tougher to tweak it into alignment. This could mean disassembly and either tweaking the gas tube external to the receiver or replacing the gas tube.

When I assemble an upper I tighten the barrel nut until it is just short of perfect alignment, but far enough where I can get the gas tube in through the barrel nut, receiver, delta assembly, etc. Then once every thing is installed, I finish tightening the barrel nut until the gas tube is floating in the slot in the barrel nut. This ensures there is no binding force on the gas tube from the barrel nut which could cause misalignment inside the receiver.
Link Posted: 8/28/2005 9:36:44 AM EDT
Thanks Mongo. I'll try bending it all little by hand first.

If I do end up needing to replace the gas tube, is that something that requires removal of the barrel and other complicated procedures? Or, does it just entail driving out the pin the the FSB and pulling the gas tube out?
Link Posted: 8/28/2005 9:52:17 AM EDT

Originally Posted By SSeric02:
Thanks Mongo. I'll try bending it all little by hand first.

If I do end up needing to replace the gas tube, is that something that requires removal of the barrel and other complicated procedures? Or, does it just entail driving out the pin the the FSB and pulling the gas tube out?



Knock out the gas tube roll pin, in the FSB. Push/pull the gas tube into the receiver. Turn it so that it clears the FSB and pull it out of the receiver. It's not too hard to do.
Link Posted: 8/28/2005 10:14:39 AM EDT
Mongo, got it. Pretty simple as I thought. Thanks again for your help. Very appreciated.
Link Posted: 8/28/2005 12:32:37 PM EDT
Not a big fan of indexing the gas tube using a screw driver inside the receiver. A little too much with the screw driver and you can mark/kink the tube.


Instead, pull the hand guards and tweak the gas tube over the barrel to straighten it out inside the receiver.
Link Posted: 8/28/2005 1:17:27 PM EDT

Originally Posted By Dano523:
Not a big fan of indexing the gas tube using a screw driver inside the receiver. A little too much with the screw driver and you can mark/kink the tube.


Instead, pull the hand guards and tweak the gas tube over the barrel to straighten it out inside the receiver.



Neither am I, but it does show up in some reference material as a possible solution. The best fix is to use in spec parts, properly assembled, as you mentioned.
Link Posted: 8/28/2005 3:44:26 PM EDT
Well, I tried to lightly bend the little bit of the gas tube that sticks into the upper. I didn't push to hard, and it's not very long, so it didn't move much if at all. Took off my RAS and tried pushing on the gas tube above the barrel, but that didn't really do anything either. So, I'm going to try replacing it now.

I'm gunna go out on a limb and assume that a gas tube from Bushmaster is just as good, albeit half the price, as one from Colt?

Link Posted: 8/28/2005 4:11:37 PM EDT
[Last Edit: 8/28/2005 4:11:51 PM EDT by j3_]
The last tube I got from them fell right in and I did not have to adjust it any. I have had problems with DPMS tubes.
Link Posted: 8/28/2005 5:45:43 PM EDT

Originally Posted By SSeric02:
Well, I tried to lightly bend the little bit of the gas tube that sticks into the upper. I didn't push to hard, and it's not very long, so it didn't move much if at all. Took off my RAS and tried pushing on the gas tube above the barrel, but that didn't really do anything either. So, I'm going to try replacing it now.

I'm gunna go out on a limb and assume that a gas tube from Bushmaster is just as good, albeit half the price, as one from Colt?




In the Colt armorer course, its stated to get it as close as possible, then bend it if needed.


I would bend the gas tube before I replaced it, the worst that happens is that it works.....
Link Posted: 8/28/2005 5:47:12 PM EDT
You could always eyeball the misalignment, remove the tube and tweak it outside of the receiver then reinstall it correctly. That would save you a little $$$$. Gas tubes don't go bad that often unless you are putting mega rounds through the upper.
Link Posted: 8/28/2005 8:06:39 PM EDT
[Last Edit: 8/28/2005 8:08:35 PM EDT by repub18]
cant he just torque the barrel nut a little more or less to line it up correctly? I had that problem with my upper and with a little adjusting of the barrel nut, it is straight as can be. That requires tools if you dont have them though.
Link Posted: 8/28/2005 8:39:42 PM EDT

Originally Posted By repub18:
cant he just torque the barrel nut a little more or less to line it up correctly? I had that problem with my upper and with a little adjusting of the barrel nut, it is straight as can be. That requires tools if you dont have them though.



We are taking for granted that the barrel nut was installed correctly, with the top two spines correctly indexed against the upper receiver gas tube channel.

But you do bring up a good point, if the barrel nut spines are not correctly indexed, the gas tube will be thrown to one side and can cause one hell of a problem.
Link Posted: 8/28/2005 10:13:27 PM EDT
I'll try removing the gas tube and bending the end just a little before I replace it.

For clarification though, the gas tube appears to come into the upper through the barrel nut straight. That pathway appears clear and straight. But, after coming into the upper about about 2-3mm, the tube bends to one side.
Link Posted: 8/29/2005 2:27:01 AM EDT

Originally Posted By SSeric02:
I'll try removing the gas tube and bending the end just a little before I replace it.

For clarification though, the gas tube appears to come into the upper through the barrel nut straight. That pathway appears clear and straight. But, after coming into the upper about about 2-3mm, the tube bends to one side.



That's typical of it contacting the barrel nut slightly, which is pushing it off to one side.
Link Posted: 8/29/2005 8:35:51 AM EDT
Hmmm. So, does this mean that I might end upo having to do some serious work on a brand new upper?
Link Posted: 8/29/2005 8:42:49 AM EDT

Originally Posted By SSeric02:
Hmmm. So, does this mean that I might end upo having to do some serious work on a brand new upper?



To me, this is not "serious" work. To others, it might be. All you are doing is removing and tweaking the gas tube if necessary, then adjusting the barrel nut so that it isn't deflecting your gas tube.
Link Posted: 8/29/2005 8:54:25 AM EDT
Removing the gas tube isn't serious to me. But, I'm living in a small apartment right now and don't have a workbench or vice, so anything requiring that kinda stuff is serious for me.

Hopefuly, I won't need to mess with the barrel nut. The hole through the upper appears clear and straight.
Link Posted: 9/3/2005 4:32:58 PM EDT
Well, I removed the gas tube this afternoon, and while it appeared quite straight, I was able to see, as several of you pointed out, that the barrel nut is ever so slightly off center and obviously exerting enough pressure to cause the receiver end of the gas tube to bend.

Through some trial and error, I was able to bend, tweak, and adjust the receiver end of the gas tube so that once installed and under the pressure of the barrel nut, the bolt carrier/gas key slide onto it smoothly and with no hang up.

Assuming it functions OK when I take it to the range, is there any reason for me to be concerned about the off-index barrel nut? Will this cause any long term functional or accuracy problem for me?

Thanks again for all the help.
Link Posted: 9/3/2005 4:54:12 PM EDT
If there's no binding, rubbing and such, you should be OK. Personally, I'd tweak the barrel nut, but I'm tooled up for that type of stuff and understand if somebody who isn't wouldn't want to do that.
Link Posted: 9/3/2005 5:17:24 PM EDT
Un fortunately I don't have a workbench or vise, so I'm hesitant to mess with the barrel nut. I'll see how it shoots and go from there. Thanks for the info and time Mongo and others.
Link Posted: 9/7/2005 11:18:43 PM EDT

Originally Posted By SSeric02:
Un fortunately I don't have a workbench or vise, so I'm hesitant to mess with the barrel nut. I'll see how it shoots and go from there.



Bad plan.

You are going to get excessive wear on one side of the gas tube as the chrome lined carrier key is harder than the stainless gas tube.
Eventually (after a long time) you will be wasting the gas that leaks past into the action and generally makes a mess inside the receiver (more than normal)
When you finally get around to fixing it the right way, you will also be replacing the parts that wore out from being too lazy to get it fixed right NOW.

The right way is to make everything align properly.

I like to remove the bolt carrier group, charging handle and gas tube and simply look through the back of the receiver.
Looking through the cloverleaf cutout for the gas tube, you will see the round hole (freefloat tube) or the two ears (regular barrel nut).
If you see the same amount of light on each side, it's right.
This is very similar to using an optical comparator, but without the advantage of magnification.
You can "SEE" very small differences when you look at it this way.

As Mongo mentioned, the gas tube WILL usually 'float' when you have everything perfect.

Randall Rausch
www.ar15barrels.com

Link Posted: 9/8/2005 5:13:04 AM EDT

Originally Posted By Randall_Rausch:

Originally Posted By SSeric02:
Un fortunately I don't have a workbench or vise, so I'm hesitant to mess with the barrel nut. I'll see how it shoots and go from there.



Bad plan.

You are going to get excessive wear on one side of the gas tube as the chrome lined carrier key is harder than the stainless gas tube.
Eventually (after a long time) you will be wasting the gas that leaks past into the action and generally makes a mess inside the receiver (more than normal)
When you finally get around to fixing it the right way, you will also be replacing the parts that wore out from being too lazy to get it fixed right NOW.

The right way is to make everything align properly.

I like to remove the bolt carrier group, charging handle and gas tube and simply look through the back of the receiver.
Looking through the cloverleaf cutout for the gas tube, you will see the round hole (freefloat tube) or the two ears (regular barrel nut).
If you see the same amount of light on each side, it's right.
This is very similar to using an optical comparator, but without the advantage of magnification.
You can "SEE" very small differences when you look at it this way.

As Mongo mentioned, the gas tube WILL usually 'float' when you have everything perfect.

Randall Rausch
www.ar15barrels.com




It's not a matter of laziness dickhead.

The barrel nut is ever so slightly off, but the gas tube is straight and the key rides smoothly onto it. Problem solved.
Link Posted: 9/10/2005 6:08:09 AM EDT
What tool do you use to drive the gas tube pin in the FS.
Desoite the holder and driver (Brownells) - it always wants to flare out.
Is there a special size needed?
Link Posted: 9/10/2005 6:33:59 AM EDT

Originally Posted By WSAR15:
What tool do you use to drive the gas tube pin in the FS.
Desoite the holder and driver (Brownells) - it always wants to flare out.
Is there a special size needed?



Two comments...

Measure across the flat of your pin.
Should be around 0.083" right?
The hole is usually around 0.078" to start with and that's just too tight so the pin flares out instead of going into the hole.

On NEW installations, I usually run a 0.081" drill bit through ONE side of the gas block and into the gas tube to make sure that the two holes are lined up and to slightly open up the hole.
This helps the pin start.
I have made my own pin starter punch, it's just a 1/4" rod, tapered to about 1/8" at the tip with a 0.087" hole drilled about 1/8" deep on the end.
This starts the pin without flaring the end.
Once you have the pin this far in, it usually only needs another 1/8" to be flush.
I use adco's gas tube pin punch for the final bottoming of the pin.

On gas tubes where I am simple re-assembling, I have not had a problem with the pin being tight and just about any roll pin punch will put the pin back into place without a problem.

Randall
Link Posted: 9/10/2005 1:13:47 PM EDT
[Last Edit: 9/10/2005 1:16:02 PM EDT by SSeric02]

Originally Posted By WSAR15:
What tool do you use to drive the gas tube pin in the FS.
Desoite the holder and driver (Brownells) - it always wants to flare out.
Is there a special size needed?



I got one of the Schuster's gas tube roll pin punches from Steve at ADCO, and one of the AR15 FSB blocks from Brownells. I could probably have improvised and done it with something else, but I've found that having the right tools makes getting a job done easier, with less hassle, and less chance of dorking it up.

The gas tube roll pin punch was only a few bucks, but the FSB block was about $35.

ETA: the one exception is, I've never used roll pin holders. Tweazers or needle-nose pliers have always worked ine for holding the pin before driving it in for me.
Link Posted: 9/11/2005 6:49:20 AM EDT
[Last Edit: 9/11/2005 6:49:46 AM EDT by WSAR15]
I used a set of Roll Pin punches from Brownells.
I like the idea of pre-drilling though... probably the right thing to have everything match.
Link Posted: 9/11/2005 10:32:34 AM EDT
tagged

viator
Link Posted: 9/11/2005 5:58:50 PM EDT
FWIW, I use standard punches, never predrill my FSB and never mushroomed a roll pin, unless some 'tard mushroomed it first. Not saying those things may not have their places, just throwing in my $0.02.
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