I am trying to remove the float tube from my AR but so far no luck.  It is the two piece type so the tube itself should unscrew from the barrel nut.  I have the the receiver mounted in vise blocks and I tried using a strap wrench but no luck.  I think the upper was originally assembled by Model 1 Sales but can't say for sure (that is what I was told at purchase).  Are float tubes normally locktited to the barrel nut?  If so, can I apply heat to the tube near the nut without ruining the finish on the receiver?  Anybody got any ideas?

Has the gas tube been removed? There will be no Loc-Tite on the barrel nut/receiver threads. Without knowing what brand of FF tube you have (or seeing a photo of it), there's no way to know if it threads onto the barrel nut, or if the barrel nut is part of it.

Without knowing the history of it, somebody could have loctited the barrel nut to the receiver.

The Model 1 tube I bought was a two piece and  threaded to the barrel nut.  You can try carefully heating the threaded area with a heat gun to expand the aluminum.  

The float tube is the two-piece type so it should unscrew from the barrel nut.  I will give heat a try.  My only concern is getting the reciever too hot and damaging the finish.  Any tips on how much heat is acceptable?

Propane can't get to hot. Any Locktite that may have been used will loosen at 300 degrees.
Try heating it up arund the nut are, it then should loosen.
Let us know how it goes.

I used a heat gun to heat up the float tube and was able to remove it with the strap wrench.  Thanks for the help.

I've got this same problem now, shouldn't these things unscrew without such a fight? I bought this used, it is beyond dirty.