I'm like 15 hours in and haven't tried to take on a horde yet and I'm about halfway through the 3rd camp. Am I behind on that aspect of the game because I was reading earlier in the thread and some people took them down within the first 6 hours and I was like wtf.
I accidently triggered one (the horde in the train car thats near the NERO checkpoint) and Im right around where you are in the story I think. I was trying to clear the check point quietly when I got rushed. I figured I would try to take them down and spent basically all of my gear doing it but it wasnt too difficult (but it did seem much smaller than some of the hordes Ive randomly crossed throughout the game so far). I did it with an SMG, upgrade 9mm pistol, and the fucking crossbow (definitely wasnt prepared).
How I did it: I would just sprint when I could, turn and fire the SMG at the crowd, or throw molotovs,grenades,pipebombs. Or I would lead them passed gas cans and explosives and use my pistol to blow them up.