@thewood1 - You don't have to ungroup them, just view them in unit-view to add the mag to the specific unit where you want it. You poor poor soul, if you've been ungrouping them just to add mags.
@JP - You can add weapons in group view (for facility groups) because it will show the all mags in the group if there is at least one, but you can not add a new magazine unless in unit-view. I just tried "I can add magazines to groups of land facilities without a SAM facility if it has an ammo facility." and as expected this is not correct, there is no add mag button when in group-view on a land group no matter what type. As others have pointed out it's been that way.
Are you sure you're not in unit-view when trying it or confusing add weapons with add magazines? The only time you can while in group-view is when it's a single-unit airbase or port, and even then if you group those with something else you'll lose the ability unless in unit-view and select the specific unit.
Here is a land group with no sam's for example.
I should be able to add a magazine to any group of facilities that have an ammo facility.
I understand the feature request desire to be able to add mags to a selected group. I don't understand saying it should only apply to things that have ammo facility specifically though, because most any facility can have a magazine added to it, a runway, a hanger, a single trooper,etc.
But let's think about the request. Say you've selected a group be it SAG or an airbase doesn't really matter, and most if not all members of that group can host magazines. Lets say the button was there, you pressed add magazine, selected the mag you wanted, it gets added. But where does it get added? Do you want it to select a member of the group at random? If the answer is yes, well that might be ok for an airbase to some degree (beyond people saying...hey it added a mag to my runway that's not realistic! waa), but for say a group of ships or a group of sam sites or any group really that is dispersed that's a problem because you don't know where it added it and it will not be 'usable' by the 'group' in most cases, airbases and ports are special cases. So that suggests 'random' isn't a great idea unless it's some fall back option. So what's another option? Well we could pop-up another windows that says, these are the members of the group, please select the unit you want the magazine you just selected added too, after you've pressed add selected or double clicked the mag entry. But I'm not sure how much gain is there vs hitting 'v' and selecting the specific unit in the first place. Now it may come to mind that it would avoid maybe having to zoom in and such and select\find each unit, but at least in the case of airbases a large percent of the time they're all named similarly so it's not like finding the right one you want in the list you'll have to scroll through is going to be that much easier, might even be harder not seeing the location. I'm interested what else comes to mind cause I definitely could be forgetting time-sync wise in the usual processes.
Just some thoughts, not opposed to the feature idea nor particularly pushing for it, just pondering how many clicks or hand ****s etc may or may not be really saved by it, maybe it would be a big gain, but also maybe not.