I use a soldering iron to loosen frozen bolts and screws. I hold the tip on the head and apply heat for two or three minutes. It works surprisingly well.
Trying to remove the big screw that holds barrel hinge in and it will not budge, little set or stop screw is out so that's not the problem, on the few videos I could find where they remove it they just unscrew it easily.. I'm using a big screwdriver and cranking on it as hard as I can and it wont budge, it looks almost like its a pin instead of screw but if so why the slotted screw head.Also tried a bit of heat didnt help.