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I was watching Star Trek: First Contact again, and one thing I noticed was the scene where Picard mows down a couple of Borg drones with a Tommy gun.
It got me wondering if the Borg could adapt to projectile weaponry. If they can't then why hasn't Starfleet started using them again specifically for anti-Borg operations?
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Probably, drones can have shield generators. One use of the ship's shields is to deflect space debris, so shields can block ballistic objects. The only question left is could the Borg put that kind of shielding on a drone. The answer would be almost certainly yes, if the the plot required it.
As for why not, bullets through bulkheads is a bad thing. You don't want your air leaking out, or the bullets bouncing around inside a room, or go through the walls and killing your neighbor, or wrecking some bit of important equipment. Projectile weapons inside a ship would almost certainly be very dangerous.
