How to unlock the ZRG 20mm in Warzone In order to unlock this gun, you have to get two headshot medals in ten different games. I’ve put together a page with the best loadout and instructions on how to unlock the ZRG 20mm in Warzone, if you fancy a few more pointers. Best ZRG 20mm loadout in Warzone I’ve picked out a single loadout for the ZRG 20mm which I feel works best for how it should be used. This long-range, high bullet velocity loadout is the one to go for with the ZRG 20mm, as otherwise its slow mobility and ADS speed will harm you far more than it’l help.