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Posted: 12/20/2003 9:26:32 PM EDT
[Last Edit: 12/20/2003 10:55:13 PM EDT by crashburnrepeat]
Alright, it's a longer story than that.  I went to the range today  to sight with my new load.  I noticed that as I took my AR (dpms extreme bull) out of the rear of the truck that the bipod was off to the left about 15-20 degrees.

I didn't think about it too much, I thought the free float handguard had unscrewed a little.  I tried to screw it back on but it is normally tight so I didn't worry about it.

After I got home I noticed that the handguard had backed out to the gas block. It's backed against it so hard that I can't screw it back down onto the barrel. It's truly jammed against it.

So I decide to take off the gas block (never done any AR work before) and take out the set screws on the bottom of the gas block and drive out the roll pin in the top and try to wiggle it a little.

So I grabbed the whole handguard and twisted it.  The whole barrel turned, handguard, block, barrel and all.

Well that panicked me a little, so I got a wrench, held the gas block stationary and twisted the handguard down off it. Once it was reseated I looked and saw the gas tube running down the LEFT SIDE OF THE BARREL. (As seen from straight above, looking down and facing the end of the barrel from the rear of the rifle)

So I take the wrench and slowly twist the GB until the gas tube is over the barrel and lined up again.  The problem is that in my zeal to get the gas block off, I pulled the gas tube roll pin and when I straightened it out, the gas tube moved a little and the holes not lining up. I have NO idea how to get this gas block off short of a sawzall so....

What do I do now? Should I take the GB off, remove the free float tube and check out the gas tube? I'm worried the barrel twists/twisted in my hands. It still twists a little via hand pressure (I'm pretty strong, most wouldn't be able to twist it I'm guessing).

Anyway, what's the next step?


[edited to clarify the description a little]
Link Posted: 12/20/2003 10:23:32 PM EDT
Another question; How does one remove a gas tube nut from a DPMS bull barrel?  It looks like it has to go off the barrel towards the muzzle but that's gonna scratch the dickens out of the barrel....

Link Posted: 12/20/2003 10:46:31 PM EDT
[Last Edit: 12/20/2003 10:52:51 PM EDT by pmoore4321]
I know I should not be laughing, but that post is hilarious.  It sounds like everything that could possibly go wrong did.  I was going to give you some advice, but I don't know where to start.  Your best quote, "Well that panicked me a little, so I got a wrench..."  On a serious note, I am sorry to hear about your gun.  I think if you had the proper barrel wrench and an action block you could have it running in about 30 minutes tops.  You may have a bent gas tube, but that can be replaced on the cheap.  You are lucky you have the gas block that is easily removeable.
Link Posted: 12/20/2003 10:52:28 PM EDT
[Last Edit: 12/20/2003 10:59:30 PM EDT by crashburnrepeat]
Thanks for the support,  I too, don't know where to start.   I guess I should learn that when I panic, not to get a wrench. [:D]  I really have not clue how to get that gas block off and I need to get that thing off because in my "troubleshooting"  which turned out to be troublemaking, I removed the gas tube roll pin.  In all the working, the tube and pin holes no longer line up.  [nuts]  so I gotta figure out how to line those up and get the pin back in there.

It would help if you told me the correct order to remove all the parts of the upper. It looks to me like you are supposed to slide the gas block off the front of the barrel but then looking at parts diagrams, the gas block seems to be part of the barrel so maybe it's not designed to be moved.  I think my block came onto the barrel from the rear because if you put it on from the front, it would scratch it all up.

It is kind of funny, or would be if it wasn't me.  I'll just have to view it as a good opportunity to get more familiar with my rifle....

I have to fix it, this thing's  to accurate to sell to someone who know's what they're doing.

Link Posted: 12/20/2003 11:10:03 PM EDT
[Last Edit: 12/20/2003 11:13:24 PM EDT by pmoore4321]
Once you loosen the screws on the gas block it should just slide forward off the barrel.  If you the gas tube is not bent real bad, you should just be able to re-pin the tube to the block and slide it back onto the barrel.  You said the barrel is loose.  I am guessing you mean there is play in the fit into the receiver.  This is where I would be worried.  You might try lining up and tightening the barrel with the proper wrench.  I would not sweat it.  There is not much on an AR-15 rifle that can't be fixed pretty easy.  
Link Posted: 12/21/2003 3:36:18 PM EDT
My guess is that you should get a new gas tube when you put it back together.  A bent gas tube may interfere with bolt/carrier operation.  The end of the gas tube in the upper receiver should be centered in the slot the charging handle and carrier key ride in.  A bent tube will likely cause the end of the tube to be off a little and may not allow proper operation.  I shot you an email.  If you could send some pics, I'm sure I could talk you through the fixing of this problem.
Link Posted: 12/21/2003 4:36:04 PM EDT

First step is to remove the gas block.  This is done by pulling the block straight out.  If needed, you can slightly twist the block to get it to slip.  The block rests on a slightly larger diameter section than the front of the barrel, so once the block releases from the gas area, it will slip off the front of the barrel without scratching the rest of the barrel. The gas tube will slightly flex, so normally I will pull the gas block and the tube as one unit.

Once you have the block/gas tube out, you will need to vise the upper up in an upper vise block.  Since the DPMS float tube is a single unit, you will need to use a band tool, or a DPMS thin profile gas tube wrench to tighten the float tube up one more gas tube hole on the float tube nut.  This is done by inserting a long rod (the size of a gas tube) inside the float tube/barrel nut and tightening up the float tube/nut until the top hole of the float nut and the upper receiver gas tube hole are aligned.

On you old tube, as long as you didn’t pinch the tube, it should be able to be straightened, and reused.
Link Posted: 12/21/2003 5:41:09 PM EDT
[Last Edit: 12/21/2003 5:42:05 PM EDT by AeroE]
Try heating the gas block with a hairdryer - the block will loosen and slide off easier, reducing your already high pucker factor.  [The coefficient of thermal expansion of the aluminum gas block is a little higher than the steel barrel, so the block will grow at a faster rate than the barrel.]
Link Posted: 12/21/2003 7:05:14 PM EDT
Originally Posted By Dano523:
Since the DPMS float tube is a single unit, you will need to use a band tool, or a DPMS thin profile gas tube wrench to tighten the float tube up one more gas tube hole on the float tube nut.  This is done by inserting a long rod (the size of a gas tube) inside the float tube/barrel nut and tightening up the float tube/nut until the top hole of the float nut and the upper receiver gas tube hole are aligned.

View Quote

By one piece tube you mean one piece all the way around, not front to back right? My Free float unscrews and leaves a little two ince piece at the rear that it unscrews from. (that is it unscrews till it hits the gas block that won't budge...)

On you old tube, as long as you didn’t pinch the tube, it should be able to be straightened, and reused.
View Quote

LOL, I think my old tube is toast. I sent Mongo001 some pictures and I think we figured out that the pin that is supposed to hold the barrel in place either sheared or was never installed.  the vibration of the truck, working on the bipod one way and the magazine/scope the other way vibrated the barrel loose.  

when I saw the bipod was misaligned, I thought the float tube had unscrewed and so cranked it back around the right way, unfortunately, I cranked it the wrong way, wrapping the gas tube ALL THE WAY AROUND the barrel (yep, you read that right).  

Incidently, it shot fine like that..... It was off about two inches to the right but I thought that I had dialed in windage at the last shoot.

anyway, I turned it back around the right way but the gas block and the barrel turn as one, very solid unit.

Mongo has also suggested I heat the GB up and try to remove it. I'll give that a crack tomorrow afternoon and let you know how it goes.

I think I'm going to have to buy a DPMS float tube wrench to get the base of the float tube off to inspect for damage.  

Will update as I progress.  Do I need a special fitting to clamp the upper vise or can I put it in a normal vise with just padding?

Link Posted: 12/22/2003 6:50:10 AM EDT
You need a "Upper vise block" to hold the upper in the vise without damaging it.

[img] http://www.brownells.com/Images/Products/231015023.jpg[/img]

[img] http://www.brownells.com/Images/Products/231000157.jpg[/img]
[url] http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=17094&title=Upper+Receiver+Block[/url]

Link Posted: 12/22/2003 6:57:57 AM EDT
The gas block on the DPMS bull barrel will, in all liklihood, be very difficult to get off if you have fired her alot.  Use a blowtorch - lightly - on the block and wack it with a hammer.  After you have removed the screws, of course.
Link Posted: 12/22/2003 5:09:12 PM EDT
I asked crash to send me a few pics and did a little trouble shooting via email.  It appears that his barrel is unthreading from the extension.  Looks as though he may have to replace the gas tube because in the twist, it looks as though it won't line up with the gas block anymore.  Minus tools necessary for the job, he probably needs a new gas block ($24 at midwayusa), gas tube and roll pin ($8-10 just about anywhere) and maybe a little touch up paint on the FF tube.  Had him heat the gas block, like AeroE said to, and cool the barrel with rags in ice water for additional clearance.  Gas block should come off with a little persuasion with the heat/cool affect - probably some crud and a burr or two holding it in place - new ones slide on and off if I am not mistaken.  

We'll get this bugger up and shooting in no time.
Link Posted: 12/22/2003 5:21:20 PM EDT
Mongo001 and everyone,  well the gas block is 2" forward now but at a pretty high cost.  The FFT is %$^&$@#.  I had to lever the gas block off by levering against the ff tube and it folded it over in a couple of places.  The gas block is still tight as all get out and I'm not sure where to go from here.

My inclination is to drill and tap the front of it,  put a slide hammer to it and drag it off the front of the barrel just to see if it can be done.  Then take the rest of it and throw it in the %$#^%$# river.  Just kidding. Sort of.

Anyway, not sure how to progress from here,  I am heating the GB and then working it off but it's far enough from the ruined float tube that I can't lever off it anymore,  but it's not far enough to get arubber mallet or anything in there.  A slide hammer might be the only option.  It's so tight it takes everything I've got to budge it with the large flat steel bars I had to use to losen it.

any further ideas?

Link Posted: 12/22/2003 9:59:17 PM EDT
[Last Edit: 12/22/2003 10:00:30 PM EDT by Kaliburz]
Put the entire unit in a chest freezer for about 1 hour and then use the hair dryer to head the gas block......

I know this works in putting diesel engine liners in blocks.... (cool liners and the drop right into a room temp block)...so says the old timer mechanic....

Hey, if you cut off the mangled section on the FFT, you "might" be able to reuse it on a 16" barrel..... after refinshing.  Cheezy...maybe...
Link Posted: 12/25/2003 5:59:09 PM EDT
The set screws or roll pins or whatever holds the gas block in place have been removed right?  If so, and it is as you describe, then one thing that may help beyond the differential temp method is to try to get some penetrating oil between the block and barrel.  Breakfree is pretty good as well as a bunch of other agents so designed for this.  It should take a couple days for the oil to fully penetrate between the block and barrel.

Once the block is off, the gas tube can then be removed.  At this point you can see if you can get the holes to line up in the block so you can reuse your tube, but from the sounds of it, it looks like you may need to get a new one.  

From the sound of it the handguard could be of two different types.  The most common uses a seperate barrel nut which threads onto the upper receiver and holds the barrel on.  This is the part the gas tube will have to go through and will need to be torqued down with a barrel wrench.  The handguard tube then threads onto the barrel nut and is tightened down with a strap wrench.  Removal would be in the reverse order.

The other sort is the where the handguard tube and barrel nut are one piece.  From the sound of it, this may be what you have.  These are a bit tricker to install and require you to torque the barrel nut portion from the other side.  I am not too familiar with this sort of handguard so I can't really go into more detail on installation and removal.
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