I found a barrel assembly that I really want.  Its a DPMS 16" bull barrel.  How hard are these to install onto an upper?  What tools are needed?

You will need a VERY Strong vise and a pair of vise jaw blocks (the type with the polymer pads are best to prevent barrel slipping).

and you will need a 3/32(I think pin punch to remove/install gas tube.

and a Barrel wrench (the one piece $30 variety
(You will need a free-float tube also (these replace your barrel nut)) and some anti sieze for the tube.

It is not difficult if your barrel nut is not siezed on the upper < mine was and it was a total whore.  I had to cut it [BBL NUT] off with a dremel tool.

Here is what is needed if you are starting with a 16" barrel upper. I you have a 20", you will need a 16" gas tube.

Barrel, float tube, gas block or sight to fit the new larger barrel.
Upper vise block(plus vise)
Barrel wrench( with torque wrench)
punch(for gas tube roll pin)
Band tool

Start off by pulling the hand guards, then clamp the upper in a upper vise block.
Punch the gas tube roll pin out, then pull the gas tube.
Using a barrel wrench, spin the barrel nut counter-clock wise to remove the nut.
Pull the barrel straight out, do not twist.

Install the bull barrel in the receiver, then use the inner float tube nut to tighten the barrel to the receiver. You will tighten the nut three times to 35 lbs on greased threads, then on the third time, once you achieve the 35 lbs, turn the nut a little more to aline the top nut hole to the receiver gas tube passage.

Using a band tool, install the tube to the barrel nut and tighten.

Install the old gas tube to the new gas block, then make a pencil mark on the barrel(at the barrel shoulder to show gas port location) to aline the block gas port to the barrel gas port. Insert the gas tube and gas block on the barrel, then insert the gas tube threw the nut/receiver gas tube passage.
once the block is aligned to the pencil line(port to port) , tighten the bottom screws on the gas block.

Pull the upper from the block and re-insert it back on the lower.

Drop a head space gauge in the chamber and check to see that the head space is correct.
Your done.


Total time 4 minutes, including time to drink a Pepsi.

I've got one that I tried to cut-off after I broke a $40 upper vise blocks(!), but I haven't been successful...yet.  Any hints on how to do this?  I've but into the nut parallel to the barrel as deep as I think I can without hitting the barrel, but it's still stuck.z

If the nut is seized, use some penetrating oil, if if loctited, use a steel tool and transfer heat to the nut.

Once the nut is lubed/bond broken, re-clamp the upper in a vise block and use a barrel tool(if it grips) or use a pipe wrench to loosen the nut.

Hope this helps.

I used Kroil on it.  I even bought a big can of Kroil so I could soak it overnight in Kroil.

It's a factory Colt, so I don't think it was loctited.  I've already tried both heat and leaving it in a freezer for a week.  The **** thing is still stuck.  I'd just buy another vise block, but with the pressure I was putting on it, I'm afraid of ruining the upper.  I spent several hours with a Dremel tool trying to cut into the barrel nut, and I've cut as much as I think I can into the nut without damaging the barrel, so I was wondering if there was something I was missing.z

You guys seem to have been there done that.  How bout this one,

What do you do if you head space is off?

Everyone says check but then what if seems to not come up.  Are you screwed at that point or what?

It is a new barrel, you install it, and use it with a new bolt, and you should not have any headspace problems.

But if headspace is not correct, there is not a lot you can do about it.  You can swap bolts around.  If headspace is too tight, you can ream the chamber.  But if it is excessive, nothing you can do.

So, if you run into a problem with new parts, you simply return the bad barrel or bolt to where you got it, and they should exchange it for you.

Let me put it this way, my vise has 7" jaws, and my standard DPMS barrel tool has a 12" handle, and fully contains the nut lugs.  
If it won't budge with the standard handle, then I add a 24" breaker bar to the the wrench.  
Given  my size,the breaker bar, and the block being fully gripped in the vice, you looking at over 400lbs of torque.  
One of two things will happen, either the nut is going to turn, of the receiver is going to shear.  Since I have not sheared a receiver yet, I have found that no nut is ever fully seized.

To bad that you are not closer, or I could have the barrel off in less than a minute.

ZOOM, if you have cut a substantial groove in the nut it will fracture easilly for you and open right up.
with the nut supported under, place a good sharp chizel into the groove you have cut completely accross the nut, and a sharp blow to the chizel will fracture the nut at the groove allowing the threads to become loose as the nut will expand slightly when fractured. prepare and one blow will split it.

Dano523, when I removed a barrel from my Hesse FAL receiver, I used a 5' breaker bar with all ~230# of my pounds on the end of it.  I barely got the barrel off, and I bent-up the metal receiver wrench.  In my first attempt, I broke my nearly 50 year-old ~8" vice.  I tried putting a portion of that same torque on the Colt AR upper, but I ruined my Bushmaster action block.  I've also knocked-off about half of the tips on the barrel nut.  The problem isn't getting enough torque.  I can already put enough on it to ruin the block and the nut.  I've already started cutting on the nut, so now I'm pretty sure I need to figure-out how to do that the right way.

ALAN308, I've already tried that with a chisel.  The metal on the nut is springy.  It didn't crack like I expected it to do.  I'll probably try that again, just because I don't know what else to try.

I'm putting together a rifle for a friend, so I'm not making anything on it.  That's also why I'm trying to save both parts.  He really can't afford to buy a new upper.  The delta ring was broken, so I'm having to take-off the barrel.  In hindsight, I should have just taped the handguards on [:)].  Because I also have to replace the nut now, I'm going to have to remove the front sight base.  This project quickly became a losing proposition.z

Unless it has a chrome lined chamber.

Zoom,
Sounds like someone used red loctite when they installed the barrel nut.

My only suggestion would be to transfer heat until the loctite bond brakes. When the bond is broken, there will be a puff of smoke that come out towards the receiver.

The easiest way would be to use a strip of metal, wrapped around the barrel nut with the ends sticking out, then punch a hole just past the wrap to inset a nut and bolt to hold the metal loop onto the nut.  After you have secured the transfer metal strip, take a Mapp torch and start heating the ends of the strip of metal to transfer the heat.
Also, depending on how hot you need to get the nut to break the bond, you may want to add some heat absorption compound to the barrel and receiver just before and after the nut.

If the nut is loctited on, even after you punch the nut, it will still be bonded onto the receiver threads. This could be the reason that you are having a hard time splitting the nut.

Hope this helps.

Why would anyone install a barrel with locktite???  It can't come off, the gas tube will prevent it from turning.  Duh!