Thanks for the replies guys!
To start with I'm just trying to get things to work in a mission as the group leader. Once I can do that, then I thought I'd have a go at a script - there's a MG crew script here on ofpec which I can use as a starting point - expect a LOT more questions when I get to that stage
The ammo crate I'm using is loaded up with the CG rounds ok - I can grab them myself, but I can't order the group member to do so. I think this may be related to the fact that the group members don't moan about being low on ammo for secondary weapons.
What I'm trying to do is use the No.2 as an 'ammo source' for the CG/MG/etc, so the AI will take care of it automatically - I can recall hearing '#8 rearm at xyz' type of chatter during missions where I was just a group member, so I figure it should be possible. But I think that was for primary ammunition - normally on that kind of mission I tend to shadow the AT/LAW guy to provide covering fire and to pick up the AT/LAW if he gets hit, otherwise the squad loses the AT capability.
I need to do a bit more investigation - it may be the only answer is to use a script, but I'm fairly clueless at the moment, so I'll have a root round here at the faqs etc.