Go to the BP_AIMasterHoldable blueprint and create a new variable called ProjectileUseWeaponDamage and set it to a Bool and set its default value to True (ticked on) then tick Instance Editable. Then copy the images below, locations at the tops of the screenshots. NOTE there are 2 places this code need to be added in the Range Attack function after the 2 SpawnActor nodes.

Feature guide

https://defusestudios.com/smart-ai-projectile-use-weapon-damage/