That's hard to do since the first 3 minutes there's no heavy ammo ;) All kidding aside, I get what you're saying. I've heard the heavy ammo announcement and looked down to see that I still had a full reload left. People get really surprised when you show up at their ammo spawn and start blasting them in the face with a heavy that shouldn't have ammo in it yet. A little ammo conservation can go a long way to ensure victory.