star trek - How come the Federation did not routinely use projectile weapons against the Borg?

In "First Contact" Picard kills a couple of Borg drones in the Holodeck with a holographic Tommy gun. It would appear that while the Borg are able to adapt to become impervious to energy weapons, they are vulnerable to bullets. This looks like a gaping logical hole: why couldn't Star Fleet replicate "primitive" assault rifles to fight the Borg, if they knew that phasers were useless against them? Has this ever been addressed?

Answer

In-universe, I would think that the use of chemical explosives and kinetic energy weapons would be SEVERELY discouraged on any starship, given the chances of a hull breach, and the security forces we typically see would be mostly useless with such weaponry. They have been trained on energy weapons without recoil, with no significant magazine capacity, no need to reload, etc. It would be like taking a group of riflemen and giving them crossbows.

From a writing standpoint, there's just no way for the Borg to be a threat once the Federation begins using firearms instead of energy weapons. Kinetic energy isn't like the magic energy weapons they use - you can't just 'shield' against it (or else punches, swords, etc wouldn't work) and the relative simplicity of even modern firearms to mass-produce (given the established technology of the replicators) would quickly render Borg useless as face-to-face villians.

And CGI battles cost money.

In short: The Federation doesn't have the training to use them well, and would end up killing many of their own (if they even considered the possibility) by using them incorrectly, and if they ever did gain widespread use, the series would lose a major antagonist.