Like other weapon-related armor mods, Holster mods are available for lots of different weapon types. These mods are not only stackable, granting an even faster full reload time, but they also work with Exotic weapons too. It seems like each weapon type can fully reload in a fixed time, so number of bullets loaded per second varies with magazine size. When slotted into a pair of boots, these mods will steadily reload stowed weapons of a certain type over time, a bit like a slower but general-purpose version of the Auto-Loading Holster weapon perk.
With Season of the Lost in Destiny 2, Bungie has introduced Holster mods for leg armor.
