Honestly, I hate advising this. This is the worst advice I could possibly give. But here it goes. Sometimes, watch adverts. Watching an ad after a mission will double your reward, and if you're really in need of a new rifle or upgrade, you can get those pretty quickly. Yeah... Adverts. thirty seconds of them. You can skip at any time, but you'll lose your reward. I know. Harsh. But you will get cash for rifles.