This feature allows you to set starting weapon’s ammo, starting weapons are the weapons the player spawns with when the game starts. To set the players starting weapons you can check the guide linked below.
In the BP_PlayerInventory you can now find the StartingWeaponAmmo setting in the Class Defaults.
You can add entries to add starting ammo to weapons set in the StartingWeapons array. Like shown in the image below.
This will give the M4A4 in the primary slot 30 ammo to start with. To effect a different weapon slots starting ammo just change the Slot in the Starting Weapon Ammo setting. You can also set ammo for both the primary and secondary starting weapons like shown in the image below.
Note – the weapons are still capped by the max ammo and the ammo item restrictions of the gun and magazine. To change these check the weapons guides in the documentation.
The Weapons Allowed Ammo setting is in the weapon’s holdable blueprint in its class defaults.