search score attack and choose gruntpocalyps get about 2.5k-3k per game depending on your commendations

go for headshots and multi kills

I agree, iv been doing this all week and got a shit ton of credits

score attack ; Gruntpocalypse
use your DMR and do the most headshots as possible, the best map is Corvette
1100-1300 Cr and 5-7min each game (without any commandations completed), do daily challenges also
forget challenges like: kill 200 grunt in campain: 1000Cr

campaign any difficulty doing just half of any lvl gets me 1k+