Don't ditch people when they get to heavy ammo first. I know it's a disapointment, but help the guy out.
If he's safe, yeah, go for the fight, but if it's pretty heavy and the enemy team is just seconds way, cover your teammate, make sure he recovers that heavy safely.
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Even better, don't shove the person who is already waiting on it. I stick with anyone I see grab heavy too. To cover and to grab the heavy IF they get killed.