Scarab gun will not pick up ammo from ammo boxes. It shows 40 bullets in clip and 0 in reserve and every time I find a ammo box and try to reload reserve ammo it will not reload. Has anyone else had this problem and if so how can I fix it. I have 360 version.

I have the same problem on the 360 except it now won't let me pick up any ammo for any assault rifle and I now have to switch my weapon for the one on the ground even if it's the same weapon to get the ammo already loaded into the weapon. I think holding the spec ops scarab and marshall at the same time messed the gun up. The glitch for me occured after the mission: dead man walking.