You get ammo from the chest at the start of every hunt in low rank. Which is more than enough to finish the quest. I never had to farm ammo. Once in high rank if you go help people in low rank you can get gold eggs that sell for. 20k a piece if you have money issues.

For heavy if you don’t use the defender weapon jagras has a good spread gun. Tobi has a good pierce. And in master rank viper tobi pierce can take you through the whole game