This is from the Destiny Strategy Guide Unique Armor Mod Effects Do Not Stack Just a warning: you can only have one of each different mod type, so if you find a reduced melee recovery piece, a second won’t reduce your recovery time further. The same goes for a grenade throwing distance boost or a health from orbs bonus. The two exceptions to this rule are ammo inventory bonuses and (potentially) reload speed. Reload speed can theoretically stack, but at the moment, you can only find it on one armor slot. Perhaps an Exotic piece down the line will remedy this! Hope this helps