Hi shotgunlover.
What I am about to describe is somewhat brutal but it has an extremely good chance of helping you remove a seized rusted and other reasons that make screw threads virtually impossible to move. It does involve heat but in a very specific way applied to the joint pin its self. You will need a stick welder not a Mig or Tig just a standard coated electrode welder capable of providing a couple of hundred amps. You attach a carbon rod (the copper coated type used for ark brazing) to each output cable of the welder then apply the carbon rods to each side of the guns hinge pin then turn on the current. You will find that the steel pin will start to heat up because the steels electrical resistance is far higher than the copper wire of the welder leads plus the carbon rods, If you keep the connection on long enough you can get the joint pin red hot. This method has been used for many years for removing rusted or generally seized bolts nuts and studs but things do get hot so not for the feint hearted!
