Was your APC buttoned? The 4FP-MG of this vehicle is a 360-degree MG (indicated by the *) that need your gunner to stick his body out of the APC, thus the APC must be unbutonned
Yep, playing lock'n load from the first forgotten heroes edition and studying about Vietnam war all my life was not enough.
I forgot the 50 calibre mg was external. Epic fail