Yes. You need to create a weapon holder and then put the weapon in it.
Let me have a look and see what I have handy.
EDIT:
This is some code I use in mission.
_whx = 7144.28
_why = 6050.29
_whz = 0.25
wH1 = "weaponHolder" createVehicle [_whx,_why,_whz]
wH1 addMagazineCargo ["M16", 4]
wH1 addWeaponCargo ["M16", 1]
wH1 setPos [_whx,_why,_whz]
wH1 setDir 230
wH2 = "weaponHolder" createVehicle [_whx,_why,_whz]
wH2 addMagazineCargo ["HandGrenade", 2]
wH2 setPos [_whx+1.3,_why+1.2,_whz]
wH2 setDir 90