If it is a 2 piece design (Free float tube, and separate barrel nut combo), then lock the upper receiver into a receiver vise block and try just rotating the free float tube, not the barrel nut.  If you can remove the free float tube, then you should be able to remove the gas tube and put a wrench onto the barrel nut to remove it from the receiver.

CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

That is the first thing I would try and see if it will move and separate from the barrel nut.

CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123  

Being that the gas block looks to be secured to the barrel via set screws,

My attack plan would be to hit the Gas block set screws with a torch until you sell a sweet smell to break any locktite bond, back the set screws out and remove the FS and gas block with gas tube off the upper first.

Then with a upper receiver in a upper vise block in a vise, would than take a band tool to the hand guard to turn it counter clockwise, to see if the tube from the barrel nut, or the barrel nut from the receiver is going to spin off first.  Hence if the barrel nut spins first, then with the gas tube in place, the gas tube is going to get bent.


If the barrel nut spins off with the float tube still tight to it, then, just use two steel pins in the vise jaws to back up the nut up through it's tube channels, Use a torch at that tube to barrel nut section to break down any loctite used there, then band strap the tube off the barrel nut.

Hence the way that I see the float tube being instead to begin with, the barrel nut was first torque to spec and indexed for the gas tube to pass through it, The gas block with tube as installed with the gas tube tweaked to index it correctly to the carrier key, then the tube lock jamb ring was threaded on all the way back, the hand guards was threaded on, leaving a gap between the two, then the tube was indexed to position, backed off a slight turn, loctite applied to the gap threads between the two,  the lock jam ring spun to the tube, then while holding the lock ring, the tube was threaded tight against it to index the tube to the needed postion (with the loctite bonding the two in position instead).  Hence when you start to spin the tube, the barrel nut is going to spin off the receiver before the loctite bond lets the tube spin from the barrel nut instead.