If you started to play after Season Two ended, you can still unlock the Grau through this in-game challenge: Get 5 kills in a minute when using an Assault Rifle 25 times. Speed, precision, and accuracy are all key to this challenge.
Grau 5.56 Assault Rifle in COD Mobile: How to Unlock in Season 6. The majority of new weapons arrive as a part of Battle Pass, and Grau 5.56 will be no different. To acquire Grau 5.56 Assault Rifle in COD Mobile, players must reach BP Tier 21 by attaining the equivalent Battle Pass XP.