IMoO/loot_tables/equipment/low_tier_items.json

{
  "pools": [
    {
      "rolls": 1,
      "entries": [
        {
          "type": "item",
          "name": "minecraft:leather_chestplate",
          "weight": 1
        },
        {
          "type": "item",
          "name": "minecraft:iron_chestplate",
          "weight": 1
        },
        {
          "type": "empty",
          "weight": 5
        }
      ]
    },
    {
      "rolls": 1,
      "entries": [
        {
          "type": "item",
          "name": "minecraft:leather_helmet",
          "weight": 1
        },
        {
          "type": "item",
          "name": "minecraft:iron_helmet",
          "weight": 1
        },
        {
          "type": "empty",
          "weight": 5
        }
      ]
    }
  ]
}