What is the fastest/most efficient way to gain credits?
doing oni base with the target designator and reverting to last save method
Co-op Campaign, get everybody else booted, get lots of headshots.
(fastest way without cheating/glitching)
Play the game.
> Play the game.
Indeed!
I’ve also heard that Firefight Matchmaking can produce some nice bounty (although I haven’t verified that myself). 
Completing challenges also helps, such as this week’s weekly challenge.
Darn! Speaking of this weeks challenge, I forgot to get mine today! I was too busy reading Halo: Cryptum in the meantime… It’s already too late anyways to even try. I’ll try and get the rest of the challenges for this week and hope to get it then.