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I have a problem I have never run into in almost a dozen ar 15 builds .
 The hand guard ( barrel nut ) is for a DPMS free float ... the one that you can't clock .
 Cannot get the gas tube to go into the reciever when the barrel nut is tight .
 A slightly used 24 in DPMS 24 bull barrel with the factory handguard ... so I know it worked one time .
I am matting it with a Aero upper , gas tube fits the hole in the upper and slides in through the nut into reciever when lose but as soon as the nut is tightened  a no go ....
  And yes I have tried a little both ways from being perfectly lined up { a little too tight - to lose }

  I am trying this with the gas tube not attached to the gas block .... and I have a drill blank  I use for a gauge that fits , but not the  %$#@  gastube .
  By eye ball when things look perfect  left - right  it seems the nut hole sits a tiny bit lower than the hole in the reciever .  Or to put in another way , it looks like the radius from the bore centerline for the nut is slightly smaller than the radius for the upper reciever gastube hole ...
 A little file work on the nut should solve this I think , but I thought o run it past some wisdom here before I start carving . 
   I did look around and didn't see my specific problem ..  oh for  a mil-spec AR 10...   lol

Edited by rck

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Try taking it in at an angle.  I've seen the flare in the end of the gas tube not fit through the four prongs in the gas tube hole in the upper, a few times.  Only way to get the tube through there is at an angle.  Good thing your tube is already out of your gas block, because it has to be, to do this.

 

Try it like the angle in the pic below (red line). 

 

Once you get it into the upper, and you lower it to get it in the gas block - if it binds on the barrel nut, you will have to notch the barrel nut.

 

 

post-7-0-20899700-1427084724_thumb.jpeg

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It wiil go through the four prongs ... and even through with the barrel nut in place just not when the the barrel nut is  tight ...As  long as the nut has a little wiggle to it it goes tight and no wiggle  a no go .

 More than likely would have had no problem with a standard barrel nut or  shorter length on the DPMS nut it would probably go ... I do think I will be filling or drilling that 1 hole to a bigger diameter. 

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  Remove some material from the Hole in the Hand Guard to let the gas tube pass through , as long as you don't go too crazy on the material removal , shouldn't be a problem . 

You can also use the next size drill bit to make that one Hole slightly larger also.

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Thanks guys , used a chain saw file to take some material off the top { outside } of the hole and that did the trick put the gas tube in a adjustable JP gas block I should now have a upper that works :) 
I had thought of using a drill bit too ... have number , letter and standard bit sets but the material at the bottom of the hole over the upper threads is very thin , so a little more time with a file and no time spent trying to clean up threads ... 
 A lot of good information on this sight .

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I should add the DPMS hand guard clears the JP gas block , makes life easier to instal gas tube and modifying  the hand guard , being used the sling swivel stud ended up  in the 11:30 spot . ....  Murphy  at work .

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Thanks guys , used a chain saw file to take some material off the top { outside } of the hole and that did the trick

 

That thing is the best invention ever.  The Dremel version is even more fun...  <thumbsup>

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