The force fields on the Borg drones and the ones on the Enterprise are completely different. The ones on the Borg drones are strictly energy based AFTER they've adapted to that particular energy. Physical objects such as bullets, swords, etc. can harm them. How do I know this? Because we've seen Borg susceptible to gunfire, melee attacks, H2H combat, etc.
Sir, I believe I'm right, thank you very much.