I usually get two to five kills off those during the course of a match, on guys popping up out of the trenches or coming around the edge of the bushes.

This might sound stupid, but did you know you can aim down the sites of the mounted machine guns just like a regular gun? It zooms in the view and keeps the gun spooled-up to avoid that 2/3 second lag when you start firing.

I did not know this until I was on my second prestige. Maybe we need a "shit that seems kind of obvious now, but you didn't realize it for a while and others may not have either" post.