Try like, at least 10 heavy ammo synths. Honestly, I try to keep 30-40 (stack of 20 at all times for my reserve). Every time you die, you lose heavy if you are wearing raid boots. You also lose leaving and returning from orbit as well as it's just really handy for many things (dropping sword bearer fast, clearing adds fast, dropping bosses fast). You can never have enough heavy synths ;)

Xbox one

Ohh nvm