I do one of 2 things:
Stay in the same area hunting the same mobs, deal with the loot droughts, but am also there when the loots pick up.
or, i hop around to different mobs, kill 5-10 of each one in diff places, and then pick a spot where I'm getting a decent return.
both of these work, for me at least
edit: ps i only do 10k ammo runs with opalo/m2100/breer/p2/p3/mk2/ep40 =D