javais posté dans un thread concernant le meme probleme et QLONG avait donné une réponse assez utile ...
Originally Posted by Qlong
Do not heat it up as you will most definitely melt the two rubber o-rings inside the flash hider.
What you experienced was the tightening of the collar between the outer barrel and hider.
Press down the release and turn the hider counter clockwise (lefty loosy) as the hider is threaded CW on the collar.
By turning it counter clockwise you will tighten the collar to the outer barrel but loosen the hider on the collar, the hider is actually tightened to the collar by the friction of two 2 rubber crush rings, the resistance you encountered most likely was the warping/twisting of the rings.
Once that's off, loosen the grub/set screw and turn the collar Clockwise as you normally would do to take off a muzzle device on an AEG.