That problem is easily solved using your primary weapon which you can equip by pressing Y/triangle when you have your sniper out. Shoot the vandals/hobgoblins, and proceed to pick up ammo bricks. It's really not going to be a big deal at all in pve. Edit: sorry for the sarcastic, douchebag response. Been dealing with idiots at work all day, so I let some of my frustration vent.