Take the bolt and carrier out and tap the back of the piston to help move it forward and out of the gas tube.

Quoted: Of course one thing that you might try is to just replace the plug and shoot it to see if you can break it loose.

Whatever you do, do not attempt to do this.  If the gas piston is locked in place and you fire the weapon, two things could happen, one is that you might get lucky and unstuck the gas piston, which would be like trying to shoot MUD out of a barrel instead of just using something like a rod and brush to clear it outta there; second is that if the piston is really stucked, gas will not have enough room inside the gas cylinder creating a preasure build up and you might end up with a sore face and a kaboombed gas cylinder.  I've seen it happen b4.
My two cents.

HUNTER.

Quoted: actually i seriously doubt you have to worry about that. the worst case should be that it simply doesn't work... if the pressure could cause the gas block to explode, how would you explain the grenade launching position on StG gas plugs?  if the piston doesn't move, the gas will either vent out of the barrel or maybe go around the piston.   an exploding gas block, i doubt

When you turn the plug to the launching position the gas port get completly closed, doesn't it?
All the the gases in that case are used to launch the grande, that's why the weapon wont cylce when you fire normal ammo while the gas plug is set in that position.  there is not gas going upbackwards when you fire a FAL with the plug in the grenade position.

About the kaboombed gas cylinder...me and a friend of mine where out on a hunting trip, he accidentaly dropped his fal into a big muddy water puddle which was like 4-5 feet deep, when he retreived his FAL the thing was covered in mud and he's like "bah fu#$ it, it's a FAL it can take it" and all he did was clear the mud out of the barrel and the ejection port, so far so good...after letting the thing just sitting out there on a sunny day for like five hours he's like "ok, let's see how it works" the rifle at that moment was completly dry so there shouldn't have been a problem...but, aparently that same muddy water found it's way into the gas cylinder thru the vents carring some mud to the inside of the gas cylinder which after being exposed to a hot southamerican sun for like 5 hours turned into "stone" locking the gas piston  in place not letting the gas piston move back (or at least not letting it move back fast enough, we'll never know) and creating a preasure build up (vents were not enough to vent all of that gas out and or the might have been plugged with mud) bottom line is that he ended up with three things, a broken handguard, a kaboombed gas cylinder and a lesson learned the hard way, which is what i'm trying you not to get exposed to. Like i said b4, just my two cents.

Also the piston could move slow enough to create room inside the gas piston giving gases enough room to create that preasure build up i'm talking about.


HUNTER.