From the FAQ of Apex. https://www.ea.com/games/apex-legends/about/frequently-asked-questions#q3
How do the Bonus Heirloom Shards work? link
When a player opens an Apex Pack, there is a <1% probability of Heirloom Shards dropping. Heirloom Shard drops do not deduct an Apex Pack from your inventory. Heirloom Sets cannot be crafted with Crafting Metals and can only be obtained by exchanging Heirloom Shards (or through a Collection Event). A player cannot open more than 500 Apex Packs without receiving Heirloom Shards (assuming the player does not own all of the available Heirloom Sets). Once a player owns all of the Heirloom Sets, the player will not be eligible for this bonus until more Heirloom Sets are added to the game.
