I've noticed in other shooting games where you don't carry ammo, they intelligently designed ammo crates or spare ammo so that right about when you're about to run out, you can replenish it. Some of these shooting games gives you the feeling that you're running out, but then somewhere along your route it replenishes you. It's just intelligent game design. But here in D2, they just leave you out to dry, like a Constipation!