okay, place the object you want to add ammo to in the mission editor. type this code into his init line:
[unitsname,"weaponname","magname"]exec "unitReammo.sqs"
unitsname = the name of your object
weaponname = name of the weapon to add
magname = name of the mags to add
e.x. [loon_1,daa_m16op,daa_m16mag] exec "unitReammo.sqs"
then copy the attached file unitReammo.sqs into your mission directory
n.b. THIS IS FOR UNITS A.K.A. MEN ONLY