
Hmm, Some Ammo perks CAN stack (Destiny)
News to me, i never paid that much attention.
Two pieces of armor with the exact same perk, ie special ammo, won't stack. However, if you have one that gives more special, and one that gives more fusion rifle ammo, they will stack (when using fusion rifle of course) since they are technically different perks.
I'm guessing this would work with sniper as well. Are there any armors that give heavy-specific ammo? I think all of mine is just bonus heavy, not weapon specific.