Tau Gun Drones have the Networked Machine Intelligence trait which gives them bonuses to ballistic skill, intelligence and perception based on the number of drones " in the squadron". How does this work in regards to hordes, considering that magnitude doesn't directly represent the number of enemies present?

Not having my book on me, I would determine - as the GM - how many drones there are in that horde, and then apply that bonus. Within reason of course.

I think every horde should come with magnitude-to-number factor as a stat. It should only be a roundabout factor but it's also helpful for descriptions by the GM: How many hormagaunts are charging? How many get killed by the bolter fire? Will they be enough to still be a threat (overwhelming trait)?

For consistency reasons a GM should always make sure he has such an approximate factor at hand. Fights that are meant to be particular epic or species that are especially dangerous might shift that number of course.

For example, in Final Sanction and Oblivion's Edge I have frequently used the 2 beings for 1 point of magnitude rule of thumb.

Alex

I'd say play it simple, assume in the case of gun drones that 1 mag = 1 drone, and give it a large bonus. No need to make the game overly complicated.

I thought about this myself and decided that for gun drone hordes, one drone would equal one magnitude. It makes sense, these things are not used in "blotting out the sun" numbers.