Warlocks have Tranversive Steps and 3 chest pieces with these perks (Starfire Protocol, Alchemist Raiments and Purifier Robes), Titans have 2 chest pieces (The Armamentarium and Twilight Garrison), Hunters however have [u][b]NONE[/b][/u].
All other exotics specify the type of weapon that will have extra heavy ammo and allow to carry less than these generic weapon type perks (example: 6 Ghorn rockets vs 7 with one of these exotics), and this perk also increase the amount of ammo for the Sleeper Stimulant from 9 to 12 (and sword ammo by 1-2, irrelevant for swords).
I don't expect you to create a Hunter exotic this late, but at least have this in consideration for Destiny 2.
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'Member when Hunters DID have Heavy Weapon armor perks?