this addMagazineCargo ["DemoCharge_Remote_Mag",1];
EDIT CSR Kryssar:
Reproduced
1] spawn blufor MH-9 (with "this addMagazineCargo ["DemoCharge_Remote_Mag",20]" in init line) and blufor rifleman
2] preview
3] get to the chopper
4] drop all mags/grenades
5] take all explosives you can from chopper bz left clicking on them in chopper incentory
6] you'll get 3 charges in inventory and 16 charges in chopper