Ok, basically. If you go into ONI sword base and get yourself set up with the target designator boost with some recommended skulls enabled (every one except iron and blind) on heroic, you can set up custom challenges to get around 100K an hour, depending on how efficient you are. If you have no life whatsoever then you can get around a million credits a day by starting said method right as you wake up. I'm not trying to ban myself so I always keep under the credit cap in the few times I have done the method. Once you set up the campaign save there are certain challenges you can finish and turn in in around 8 minutes. Repeat this and profit. But I would suggest not making above 135K a day if you don't want to get a banhammer halfway up your digestional track. Seeing as your technically using tools that 343 gave you and cant be punished for it as long as you dont go above the cap.