You don't say whether this stuck bullet is cast or jacketed or what caliber or gun ? Personally I would never hit a brass squib rod with one of my good nylon faced hammers unless I justed wanted ruin a good hammer face. A properly sized squib rod should be as close to bore diameter as possible to avoid further obturating or expanding the bullet or making a offset hit. A light hammer just makes the job more difficult. A good size hammer with weight, good fitting brass rod and a good whack with Kroil as stated will usually get things started. Remember banging a soft engraved bullet out backwards ( only way on a revolver ) means you are usually stripping lead across the lands which makes the first twist of rifling or two the hardest
Good luck