Parameters and Values

First of all, set all values in the WeaponControllers script - Animations, Sounds, Attacks parameters, etc.

Points and Colliders

In this step, you should adjust the weapon collider.

Then, go to the weapon prefab and adjust the position of "AttackSpawnPoint", "ShellSpawnPoint", "AttackCollider" (depending on the attack in your weapon).

Attack and Shell Points
Damage Collider


Then adjust the hands and weapon with the IK system: