I have never had any success freeing a stuck brake drum with a soft
faced hammer.  I use a 6# single jack while adding a bit of outward
force with a large screwdriver or pinch bar wedged between the drum and
the backing plate.  To free it you've got to set up enough vibration to
break the rust loose.

As always, YMMV, but it's worked for me for thirty years.

Jim