OT: Darn &?%#@%! screw!!!

Hello,

Sorry, I'm OT but I need help! I am trying to disassemble a Mauser 93 rifle purchased recently for cleaning. The trigger guard front screw is stuck to death and refuses to yield. Over the past few days I have tried repeatedly to unscrew it, have used liberaly WD 40 on head (on screw head, not mine...)to no avail. Using boiling water to heat it will probably mar the finish and wood. Don't want to apply too much pressure to avoid breaking the screw either. Any suggestions? Thanks.