I think things are getting a bit heated here...and this is a bit of a tricky topic.
I've been thumbing through the core rulebook and "house of" books that I own (delaque and escher), and I'm starting to lean towards rules as written gangers/juves/specialists don't get access to ammo not present on their house list.
I also feel that gangs written before the "house of" books are approaching unplayable in the current system. Will they ever get a revision? Probably not.
I do feel that rules as intended that ammo was probably supposed to be wargear, as the range of models--leaders and champs--that can use ammo are so narrow and unlikely to do so as they will be equipped with better guns.
Unfortunately, if this is the case, then grenade launchers on specialists are a bit weaker as they usually have pretty narrow access to grenade launcher ammo. It further pushes autoguns to being inferior to lasguns--the upgrades for lasguns are definitely wargear. Shotguns go from a nice, scaling weapon to pretty meh as gangers usually only have base ammo access.
I'm aware of the paradigm shift from gangers/juves/specialists being the core of gangs to faceless henchman that are just kind of there (I personally don't like this change from oldmunda, but here we are).
However, as I alluded to before, we're free to change anything we don't like as long as they playgroup/arbiter agrees. Therefore, regardless of what the actual rule is, I don't think it really matters that much. Necromunda isn't a competitive game, nor is it a "kill team" type game where you're trying to min/max a list. You could certainly play it that way, but I feel it will ultimately be unfun that way.
To me Necromunda about watching your gang progress and creating combos and synergies with weapons and skills. I feel that putting barriers up from doing "cool things" is a bit antithetical to the spirit of what Necromunda is/was/supposed to be.