Reminds me of another annoying feature of vehicles.
You want one of your men to drop a weapon so you can pick it up, but, you can't order him to drop it because the only thing you can tell him to do with it is put it in some vehicle about a million miles away.
Planck
Actually, if you're the group leader, you can simply open up the map, go to the Gear section of your little notepad-thingy, and next to all their weapons and equipment there's a tiny little arrow (pointing down). Click that, and they'll get the order to drop their weapon (or magazine, or binoculars, or LAW) right there and then.
It's a bitch having them drop stuff like handgrenades and whatnot though, since you have to give a radio command for every one, but it's fairly quick. Quicker than having them put stuff in cars millions of miles away anyway
Just thought I'd add that little tidbit.
I've also experimented with the Rearm command in the past (can be accessed with an action ["REARM", vehicle] too, I think), but as far as I can tell it doesn't do diddly squat with AI. Didn't know it works for human players though! Planck's solution to have them put the weapon in the car and then pick it up again seems to me to be the most useable option for quick rearming. Maybe it works for rifles with attached grenadelaunchers too? At least if you pick up a GL-toting gun from a truck as a human player, any empty slots you have will fill up with Grenades and clips.
Ah well. I guess it's always possible to script in a custom addaction/radio command/doodad of some kind to give ya some quick rearming, if you can be arsed.
Good luck, anyways!
/Wolfrug out.