So after I beat the campaign with my friend on insane while having 16777300 grenades and ammo, the co-op achievement didn't unlock. Does anyone know how to fix it? Since you guys know more about this mechanics than I do.
I got this achievement without doing any funky thing. My friend came over to my place and we're split-screen the whole GoW1 in hard, across few sessions (I recalled the 3rd/4th time he visited me and then we beat the game together) Sound like you missed some of the chapter with playing co-op? Maybe you try to recalled which chapter are those and replay on co-op mode will do.
Basically, I would check and see if I missed any Chapters. If you did, then play them again! -illuminati
or just use a achievement unlocker that works to if u used 16777300 gernades it shouldn't be a problem
