Honestly, I don't see how I could have messed anything up with the drill bit action (I've since opened things up) but after I'd pulled the bit of filament by (but not in) the gears I still can't get anything through.

2016-09-26 19.18.41.jpg

Even if I'd done something fairly catastrophic with the drill bit, I'm still not getting through that tube and down to the gears. So there had to be more to it than that.