It's the non-rail free float tube that comes standard on the LR308.  

Does it just screw off?  Clamp the upper and use a strap wrench?  

Thanks.

Not familiar enough with the particular item to advise well.

Be aware of possible anti-rotation devices and that some manufactures do have specialty wrenches for their tubes.

Might want to contact DPMS.

YHM sent me some instructions when I bought one of their products used and needed them.

If it's the handguard I'm thinking of, you'll notice a seam about 2" from teh rear of the tube.  The area behind that is the barrel nut and the area in front of it is just a tube.  The front section simply screws on and off, but likely has some loctite applied.

Use a strap wrench on the front section.  If it won't come off then use a torch to heat just the front section.  Aluminum conducts heat very well so you'll need to heat the tube section quickly and get it off before too much of the heat transfers into the nut section.  Heat will also loosen any loctite that was used.  If heat and a strap wrench won't get it, you can wrap the tube in leather (or just skip the leather if you don't care about ever using it again) and use a large pipe wrench.

Once you get the tube section off, teh barrel nut section has a bunch of holes on teh front and can be removed using any standard barrel wrench.

I did notice the seam you are talking about.  

I'll try a strap wrench and will also heat the tube a little.  I have two armorer's wrenches to try on the nut.  

The tube looks like it should just clear the gas block without having to remove it also.  

Thanks for the help.  

I'll post an update after I have a go at it.  

Update

A strap wrench and a little heat from a propane torch and the tube unscrewed right off.  

The barrel nut was actually not all that tight and also came off with just the strap wrench, not barrel wrench necessary.  

Now I just have to find a good gunsmith to reprofile my barrel.  

I'm having the same problem with the tube type and a 4-rail and no luck with a strap wrench cold. Instead of the torch heat applied, I wonder if simply putting it in an oven set at 200-300 or so for a few minutes would loosen it. Also, isn't there a lock ring at the rear of the HG section threaded onto the barrel nut also that needs to be loosened first? What did you find magnum_99, HG and barrel nut or also lock ring?

Quoted: I'm having the same problem with the tube type and a 4-rail and no luck with a strap wrench cold. Instead of the torch heat applied, I wonder if simply putting it in an oven set at 200-300 or so for a few minutes would loosen it.

Depends.  If the railed tube section is aluminum and the barrel nut it threads onto is steel then it should work well because aluminum heats faster and expands faster as it heats when compared to steel.  But if both parts are aluminum then they will expand at the same rate.  In that case you'll want to use a torch to dump a lot of heat into the rear of the tube and work quicklty to remove it before the heat transfers into the nut.

If loctite was used then you will need to get it hot enough to melt the loctite.  And oven may be able to do that but since it heats the entire part it will take much longer to heat and you're stuck trying to take a 400 degree part out of the oven, clamped into a vice and the part loosened all before it cools down too much.

Best advise is to go to Walmart and spend the 10 or 20 bucks on a cheap propane torch.

Also, isn't there a lock ring at the rear of the HG section threaded onto the barrel nut also that needs to be loosened first?

 Not on the DPMS free float tube or on the similar designs from places like Bushmaster or Hogue.  Locking rings and similar mechanisms are needed for railed handguards because you need to be able to keep the rails on top, bottom and sides.  When you don't have rails you just thread it on and it tightens against a shoulder on the barrel nut.

When removing railed handguards you need to loosen any locking rings or other locking devices before trying to remove it.

Hey thanks Hoplophile....what I needed to know and more.